Error & Nullability Spam

src/main/java/io/github/skippyall/minions/MinionMixinConfigPlugin.java

@@ -1,6 +1,7 @@
 package io.github.skippyall.minions;
 
 import net.fabricmc.loader.api.FabricLoader;
+import org.jspecify.annotations.Nullable;
 import org.objectweb.asm.tree.ClassNode;
 import org.spongepowered.asm.mixin.extensibility.IMixinConfigPlugin;
 import org.spongepowered.asm.mixin.extensibility.IMixinInfo;
@@ -15,6 +16,7 @@ public class MinionMixinConfigPlugin implements IMixinConfigPlugin {
     }
 
     @Override
+    @Nullable
     public String getRefMapperConfig() {
         return null;
     }
@@ -34,6 +36,7 @@ public class MinionMixinConfigPlugin implements IMixinConfigPlugin {
     public void acceptTargets(Set<String> myTargets, Set<String> otherTargets) {}
 
     @Override
+    @Nullable
     public List<String> getMixins() {
         return null;
     }

src/main/java/io/github/skippyall/minions/Minions.java

@@ -10,7 +10,8 @@ import io.github.skippyall.minions.registration.MinionRegistration;
 import net.fabricmc.api.ModInitializer;
 import net.fabricmc.fabric.api.command.v2.CommandRegistrationCallback;
 import net.fabricmc.fabric.api.event.lifecycle.v1.ServerLifecycleEvents;
-import net.fabricmc.fabric.api.resource.ResourceManagerHelper;
+import net.fabricmc.fabric.api.resource.v1.ResourceLoader;
+import net.minecraft.resources.Identifier;
 import net.minecraft.server.packs.PackType;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -40,6 +41,6 @@ public class Minions implements ModInitializer {
 
         PolymerResourcePackUtils.addModAssets(Minions.MOD_ID);
 
-        ResourceManagerHelper.get(PackType.SERVER_DATA).registerReloadListener(new DocsManager());
+        ResourceLoader.get(PackType.SERVER_DATA).registerReloadListener(Identifier.fromNamespaceAndPath(Minions.MOD_ID, "docs"), new DocsManager());
     }
 }

src/main/java/io/github/skippyall/minions/MinionsConfig.java

@@ -11,13 +11,14 @@ import com.electronwill.nightconfig.core.serde.annotations.SerdeComment;
 import com.electronwill.nightconfig.toml.TomlFormat;
 import com.electronwill.nightconfig.toml.TomlParser;
 import net.fabricmc.loader.api.FabricLoader;
+import org.jspecify.annotations.Nullable;
 
 import java.io.IOException;
 import java.nio.file.Files;
 import java.nio.file.Path;
 
 public class MinionsConfig {
-    private static MinionsConfig INSTANCE;
+    private static @Nullable MinionsConfig INSTANCE;
 
     public Minion minion = new Minion();
 

src/main/java/io/github/skippyall/minions/block/MinionsBlockItem.java

@@ -1,20 +1,30 @@
-package io.github.skippyall.minions.block.miniontrigger;
+package io.github.skippyall.minions.block;
 
 import eu.pb4.polymer.core.api.item.PolymerBlockItem;
 import eu.pb4.polymer.resourcepack.api.PolymerResourcePackUtils;
+import io.github.skippyall.minions.polymer.VersionSync;
 import net.fabricmc.fabric.api.networking.v1.context.PacketContext;
 import net.minecraft.core.HolderLookup;
 import net.minecraft.resources.Identifier;
 import net.minecraft.world.item.Item;
 import net.minecraft.world.item.ItemStack;
 import net.minecraft.world.level.block.Block;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.Nullable;
 
-public class MinionTriggerBlockItem extends PolymerBlockItem {
-    public MinionTriggerBlockItem(Block block, Properties settings, Item polymerItem) {
+public class MinionsBlockItem extends PolymerBlockItem {
+    public MinionsBlockItem(Block block, Properties settings, Item polymerItem) {
         super(block, settings, polymerItem, true);
     }
 
+    @Override
+    public Item getPolymerItem(ItemStack itemStack, PacketContext context) {
+        if(VersionSync.isOnClient(context)) {
+            return this;
+        } else {
+            return super.getPolymerItem(itemStack, context);
+        }
+    }
+
     @Override
     public @Nullable Identifier getPolymerItemModel(ItemStack stack, PacketContext context, HolderLookup.Provider lookup) {
         if(PolymerResourcePackUtils.hasMainPack(context)) {

src/main/java/io/github/skippyall/minions/block/input/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package io.github.skippyall.minions.block.input;
+
+import org.jspecify.annotations.NullMarked;

src/main/java/io/github/skippyall/minions/block/instruction_bound/InstructionBoundBlockEntity.java

@@ -9,12 +9,13 @@ import net.minecraft.server.level.ServerLevel;
 import net.minecraft.world.level.block.entity.BlockEntity;
 import net.minecraft.world.level.block.entity.BlockEntityType;
 import net.minecraft.world.level.block.state.BlockState;
+import org.jspecify.annotations.Nullable;
 
 import java.util.Optional;
 import java.util.UUID;
 
 public abstract class InstructionBoundBlockEntity<L extends BlockEntityMinionListener<?>> extends BlockEntity {
-    protected UUID minionUuid;
+    protected @Nullable UUID minionUuid;
     protected String instructionName = "";
 
     public InstructionBoundBlockEntity(BlockEntityType<?> type, BlockPos pos, BlockState state) {
@@ -56,7 +57,7 @@ public abstract class InstructionBoundBlockEntity<L extends BlockEntityMinionLis
         return Optional.empty();
     }
 
-    public UUID getMinionUuid() {
+    public @Nullable UUID getMinionUuid() {
         return minionUuid;
     }
 
@@ -72,7 +73,7 @@ public abstract class InstructionBoundBlockEntity<L extends BlockEntityMinionLis
         return getMinion().flatMap(this::getInstruction);
     }
 
-    public L getListener() {
+    public @Nullable L getListener() {
         return BlockEntityMinionListener.getListener(level, worldPosition, minionUuid, getListenerClass());
     }
 }

src/main/java/io/github/skippyall/minions/block/instruction_bound/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package io.github.skippyall.minions.block.instruction_bound;
+
+import org.jspecify.annotations.NullMarked;

src/main/java/io/github/skippyall/minions/block/miniontrigger/MinionTriggerBlock.java

@@ -36,7 +36,8 @@ import net.minecraft.world.level.block.state.properties.BooleanProperty;
 import net.minecraft.world.level.redstone.Orientation;
 import net.minecraft.world.phys.shapes.CollisionContext;
 import net.minecraft.world.phys.shapes.VoxelShape;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.NullMarked;
+import org.jspecify.annotations.Nullable;
 
 public class MinionTriggerBlock extends InstructionBoundBlock implements PolymerBlock, PolymerClientDecoded, BlockWithElementHolder {
     public static final MapCodec<MinionTriggerBlock> CODEC = simpleCodec(MinionTriggerBlock::new);
@@ -70,6 +71,7 @@ public class MinionTriggerBlock extends InstructionBoundBlock implements Polymer
     }
 
     @Override
+    @NullMarked
     protected void neighborChanged(BlockState state, Level world, BlockPos pos, Block sourceBlock, @Nullable Orientation wireOrientation, boolean notify) {
         if(!canSurvive(state, world, pos)) {
             dropResources(state, world, pos);
@@ -105,7 +107,7 @@ public class MinionTriggerBlock extends InstructionBoundBlock implements Polymer
     }
 
     @Override
-    public BlockState getPolymerBlockState(BlockState state, PacketContext context) {
+    public BlockState getPolymerBlockState(BlockState state, @Nullable PacketContext context) {
         return VersionSync.isOnClient(context) ? state : net.minecraft.world.level.block.Blocks.COMPARATOR.defaultBlockState().setValue(DiodeBlock.POWERED, state.getValue(POWERED));
     }
 

src/main/java/io/github/skippyall/minions/block/miniontrigger/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package io.github.skippyall.minions.block.miniontrigger;
+
+import org.jspecify.annotations.NullMarked;

src/main/java/io/github/skippyall/minions/block/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package io.github.skippyall.minions.block;
+
+import org.jspecify.annotations.NullMarked;

src/main/java/io/github/skippyall/minions/clipboard/ClipboardItem.java

@@ -14,7 +14,7 @@ import net.minecraft.world.item.ItemStack;
 import net.minecraft.world.item.Items;
 import net.minecraft.world.item.TooltipFlag;
 import net.minecraft.world.level.Level;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.Nullable;
 
 public class ClipboardItem extends Item implements PolymerItem {
     public ClipboardItem(Properties settings) {

src/main/java/io/github/skippyall/minions/clipboard/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package io.github.skippyall.minions.clipboard;
+
+import org.jspecify.annotations.NullMarked;

src/main/java/io/github/skippyall/minions/command/SpawnSubcommand.java

@@ -10,6 +10,7 @@ import net.minecraft.commands.CommandSourceStack;
 import net.minecraft.commands.arguments.coordinates.Coordinates;
 import net.minecraft.commands.arguments.coordinates.Vec3Argument;
 import net.minecraft.server.permissions.Permissions;
+import org.jspecify.annotations.Nullable;
 
 import static net.minecraft.commands.Commands.argument;
 import static net.minecraft.commands.Commands.literal;
@@ -48,7 +49,7 @@ public class SpawnSubcommand {
                             ))
             );
 
-    public static int spawnCommand(CommandSourceStack source, String minion, Coordinates pos, boolean force) throws CommandSyntaxException {
+    public static int spawnCommand(CommandSourceStack source, String minion, @Nullable Coordinates pos, boolean force) throws CommandSyntaxException {
         MinionData data = MinionArgument.parse(source.getServer(), minion);
         MinionFakePlayer.spawnMinion(data, source.getLevel(), pos != null ? pos.getPosition(source) : null, pos != null ? pos.getRotation(source) : null, force);
         return 0;

src/main/java/io/github/skippyall/minions/command/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package io.github.skippyall.minions.command;
+
+import org.jspecify.annotations.NullMarked;

src/main/java/io/github/skippyall/minions/docs/DocsManager.java

@@ -3,7 +3,7 @@ package io.github.skippyall.minions.docs;
 import com.google.gson.JsonParseException;
 import com.mojang.serialization.JsonOps;
 import io.github.skippyall.minions.Minions;
-import net.fabricmc.fabric.api.resource.SimpleResourceReloadListener;
+import net.fabricmc.fabric.api.resource.v1.reloader.SimpleReloadListener;
 import net.minecraft.core.Holder;
 import net.minecraft.network.chat.ClickEvent;
 import net.minecraft.network.chat.Component;
@@ -16,9 +16,10 @@ import net.minecraft.server.dialog.MultiActionDialog;
 import net.minecraft.server.dialog.action.StaticAction;
 import net.minecraft.server.level.ServerPlayer;
 import net.minecraft.server.packs.resources.Resource;
-import net.minecraft.server.packs.resources.ResourceManager;
 import net.minecraft.util.StrictJsonParser;
 import net.minecraft.util.Tuple;
+import org.jspecify.annotations.Nullable;
+
 import java.io.IOException;
 import java.io.Reader;
 import java.util.ArrayList;
@@ -27,14 +28,12 @@ import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
-import java.util.concurrent.CompletableFuture;
-import java.util.concurrent.Executor;
 
-public class DocsManager implements SimpleResourceReloadListener<Tuple<Map<Identifier, DocsEntry>, DocsTree>> {
-    private static Map<Identifier, DocsEntry> docs;
-    private static DocsTree tree;
+public class DocsManager extends SimpleReloadListener<Tuple<Map<Identifier, DocsEntry>, DocsTree>> {
+    private static @Nullable Map<Identifier, DocsEntry> docs;
+    private static @Nullable DocsTree tree;
 
-    public static DocsTree getTree() {
+    public static @Nullable DocsTree getTree() {
         return tree;
     }
 
@@ -87,57 +86,55 @@ public class DocsManager implements SimpleResourceReloadListener<Tuple<Map<Ident
         );
     }
 
-    public static DocsEntry getDocsEntry(Identifier id) {
-        return docs.get(id);
-    }
-
-    public static Collection<Identifier> getDocsEntryIds() {
-        return docs.keySet();
-    }
-
-    @Override
-    public CompletableFuture<Tuple<Map<Identifier, DocsEntry>, DocsTree>> load(ResourceManager resourceManager, Executor executor) {
-        return CompletableFuture.supplyAsync(() -> {
-            Map<Identifier, Resource> resources = resourceManager.listResources("docs", id -> id.getNamespace().equals(Minions.MOD_ID) && id.getPath().endsWith(".json"));
-
-            final DocsTree.BranchElement[] root = {null};
-            Map<Identifier, DocsEntry> docsEntries = new HashMap<>();
-            resources.forEach((id, resource) -> {
-                try(Reader reader = resource.openAsReader()) {
-                    if(id.getPath().equals("docs/tree.json")) {
-                        DocsTree.BranchElement.CODEC.decode(JsonOps.INSTANCE, StrictJsonParser.parse(reader))
-                                .ifSuccess(entry -> root[0] = entry.getFirst())
-                                .ifError(error -> Minions.LOGGER.warn("Could not parse docs tree {}: {}", id, error.message()));
-                    } else {
-                        Identifier docId = Identifier.fromNamespaceAndPath(id.getNamespace(), id.getPath().substring("docs/".length(), id.getPath().length() - ".json".length()));
-                        DocsEntry.CODEC.decode(JsonOps.INSTANCE, StrictJsonParser.parse(reader))
-                                .ifSuccess(entry -> docsEntries.put(docId, entry.getFirst()))
-                                .ifError(error -> Minions.LOGGER.warn("Could not parse docs entry {}: {}", id, error.message()));
-                    }
-                } catch (IOException | JsonParseException e) {
-                    Minions.LOGGER.warn("Could not read file {}", id, e);
-                }
-            });
-            if(root[0] != null) {
-                DocsTree tree = new DocsTree(root[0]);
-                return new Tuple<>(docsEntries, tree);
-            } else {
-                return new Tuple<>(docsEntries, null);
-            }
-        }, executor);
-    }
-
-    @Override
-    public CompletableFuture<Void> apply(Tuple<Map<Identifier, DocsEntry>, DocsTree> o, ResourceManager resourceManager, Executor executor) {
-        return CompletableFuture.supplyAsync(() -> {
-            docs = o.getA();
-            tree = o.getB();
+    public static @Nullable DocsEntry getDocsEntry(Identifier id) {
+        if(docs != null) {
+            return docs.get(id);
+        } else {
             return null;
-        });
+        }
+    }
+
+    public static @Nullable Collection<Identifier> getDocsEntryIds() {
+        if (docs != null) {
+            return docs.keySet();
+        } else {
+            return null;
+        }
     }
 
     @Override
-    public Identifier getFabricId() {
-        return Identifier.fromNamespaceAndPath(Minions.MOD_ID, "docs");
+    public Tuple<Map<Identifier, DocsEntry>, DocsTree> prepare(SharedState state) {
+        Map<Identifier, Resource> resources = state.resourceManager().listResources("docs", id -> id.getNamespace().equals(Minions.MOD_ID) && id.getPath().endsWith(".json"));
+
+        final DocsTree. @Nullable BranchElement[] root = {null};
+        Map<Identifier, DocsEntry> docsEntries = new HashMap<>();
+        resources.forEach((id, resource) -> {
+            try(Reader reader = resource.openAsReader()) {
+                if(id.getPath().equals("docs/tree.json")) {
+                    DocsTree.BranchElement.CODEC.decode(JsonOps.INSTANCE, StrictJsonParser.parse(reader))
+                            .ifSuccess(entry -> root[0] = entry.getFirst())
+                            .ifError(error -> Minions.LOGGER.warn("Could not parse docs tree {}: {}", id, error.message()));
+                } else {
+                    Identifier docId = Identifier.fromNamespaceAndPath(id.getNamespace(), id.getPath().substring("docs/".length(), id.getPath().length() - ".json".length()));
+                    DocsEntry.CODEC.decode(JsonOps.INSTANCE, StrictJsonParser.parse(reader))
+                            .ifSuccess(entry -> docsEntries.put(docId, entry.getFirst()))
+                            .ifError(error -> Minions.LOGGER.warn("Could not parse docs entry {}: {}", id, error.message()));
+                }
+            } catch (IOException | JsonParseException e) {
+                Minions.LOGGER.warn("Could not read file {}", id, e);
+            }
+        });
+        if(root[0] != null) {
+            DocsTree tree = new DocsTree(root[0]);
+            return new Tuple<>(docsEntries, tree);
+        } else {
+            return new Tuple<>(docsEntries, null);
+        }
+    }
+
+    @Override
+    public void apply(Tuple<Map<Identifier, DocsEntry>, DocsTree> o, SharedState state) {
+        docs = o.getA();
+        tree = o.getB();
     }
 }

src/main/java/io/github/skippyall/minions/docs/DocsTree.java

@@ -3,6 +3,7 @@ package io.github.skippyall.minions.docs;
 import com.mojang.datafixers.util.Either;
 import com.mojang.serialization.Codec;
 import net.minecraft.resources.Identifier;
+import org.jspecify.annotations.Nullable;
 
 import java.util.HashMap;
 import java.util.List;
@@ -35,9 +36,9 @@ public class DocsTree {
     }
 
     public static abstract sealed class Element {
-        private BranchElement parent;
+        private @Nullable BranchElement parent;
 
-        public BranchElement getParent() {
+        public @Nullable BranchElement getParent() {
             return parent;
         }
 
@@ -45,12 +46,20 @@ public class DocsTree {
             this.parent = parent;
         }
 
-        public DocElement next() {
-            return parent.next(this);
+        public @Nullable DocElement next() {
+            if (parent != null) {
+                return parent.next(this);
+            } else {
+                return null;
+            }
         }
 
-        public DocElement previous() {
-            return parent.previous(this);
+        public @Nullable DocElement previous() {
+            if (parent != null) {
+                return parent.previous(this);
+            } else {
+                return null;
+            }
         }
     }
 
@@ -101,7 +110,7 @@ public class DocsTree {
             };
         }
 
-        public DocElement next(Element current) {
+        public @Nullable DocElement next(Element current) {
             int nextIndex = e.indexOf(current) + 1;
             if(nextIndex < e.size()) {
                 return switch (e.get(nextIndex)) {
@@ -117,7 +126,7 @@ public class DocsTree {
             }
         }
 
-        public DocElement previous(Element current) {
+        public @Nullable DocElement previous(Element current) {
             int previousIndex = e.indexOf(current) - 1;
             if(previousIndex >= 0) {
                 return switch (e.get(previousIndex)) {

src/main/java/io/github/skippyall/minions/docs/ReferenceEntry.java

@@ -15,6 +15,7 @@ import net.minecraft.server.dialog.body.DialogBody;
 import net.minecraft.server.dialog.body.ItemBody;
 import net.minecraft.server.dialog.body.PlainMessage;
 import net.minecraft.world.item.Item;
+import org.jspecify.annotations.Nullable;
 
 import java.util.ArrayList;
 import java.util.List;
@@ -55,7 +56,7 @@ public record ReferenceEntry(Metadata metadata, ResourceKey<?> object, Component
         return bodyElements;
     }
 
-    public GuiDisplay getObjectDisplay(RegistryAccess manager) {
+    public @Nullable GuiDisplay getObjectDisplay(RegistryAccess manager) {
         GuiDisplay display = GuiDisplay.DEFAULT_DISPLAY;
         if(object.isFor(Registries.ITEM) || object.isFor(Registries.BLOCK)) {
             Item item;

src/main/java/io/github/skippyall/minions/docs/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package io.github.skippyall.minions.docs;
+
+import org.jspecify.annotations.NullMarked;

src/main/java/io/github/skippyall/minions/gui/MinionLookGui.kt

@@ -20,7 +20,7 @@ import net.minecraft.world.inventory.MenuType
 import net.minecraft.world.item.ItemStack
 import net.minecraft.world.item.Items
 import net.minecraft.world.item.component.ResolvableProfile
-import java.util.Optional
+import java.util.*
 
 class MinionLookGui(
     viewer: ServerPlayer,
@@ -93,7 +93,7 @@ class MinionLookGui(
     fun openSkinGui() {
         scope.launch {
             val profile = currentSkinProvider.openSkinMenu(this@MinionLookGui).await()
-            val skin = profile.resolveProfile(viewer.level().server.services().profileResolver()).await()
+            val skin = profile?.resolveProfile(viewer.level().server.services().profileResolver())?.await()
 
             data.skin = Optional.ofNullable(skin?.properties())
 

src/main/java/io/github/skippyall/minions/gui/PaginatedList.java

@@ -6,6 +6,7 @@ import net.minecraft.core.IdMap;
 import net.minecraft.network.chat.Component;
 import net.minecraft.world.inventory.MenuType;
 import net.minecraft.world.item.Items;
+import org.jspecify.annotations.Nullable;
 
 import java.util.List;
 import java.util.concurrent.CompletableFuture;
@@ -18,7 +19,7 @@ public class PaginatedList extends MinionsGui {
     private final Component title;
     private final int size;
     private final BiFunction<Integer, PaginatedList, GuiElementBuilder> display;
-    private Runnable onClose = null;
+    private @Nullable Runnable onClose = null;
 
     public PaginatedList(MinionsGui parent, Component title, int size, BiFunction<Integer, PaginatedList, GuiElementBuilder> display) {
         super(parent);

src/main/java/io/github/skippyall/minions/gui/input/Result.java

@@ -1,7 +1,6 @@
 package io.github.skippyall.minions.gui.input;
 
-import org.jetbrains.annotations.NotNull;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import java.util.Optional;
 import java.util.function.Consumer;
@@ -27,7 +26,7 @@ public sealed interface Result<T, E> permits Result.Success, Result.Error {
 
     static <T, E> Result<T, E> ofNullable(@Nullable T value, E error) {
         if(value != null) {
-            return new Success<>(value);
+            return new Success<T, E>(value);
         } else {
             return new Error<>(error);
         }
@@ -35,7 +34,7 @@ public sealed interface Result<T, E> permits Result.Success, Result.Error {
 
     static <T, E> Result<T, E> ofNullable(@Nullable T value, Supplier<E> error) {
         if(value != null) {
-            return new Success<>(value);
+            return new Success<T, E>(value);
         } else {
             return new Error<>(error.get());
         }
@@ -49,13 +48,13 @@ public sealed interface Result<T, E> permits Result.Success, Result.Error {
 
     E getErrorOrThrow();
 
-    @NotNull Optional<T> getOptional();
+    Optional<T> getOptional();
 
-    @NotNull Optional<E> getOptionalError();
+    Optional<E> getOptionalError();
 
-    void ifSuccess(@NotNull Consumer<T> handler);
+    void ifSuccess(Consumer<T> handler);
 
-    void ifError(@NotNull Consumer<Error<T, E>> handler);
+    void ifError(Consumer<Error<T, E>> handler);
 
     <U> Result<U,E> map(Function<T, U> mapper);
 
@@ -75,7 +74,7 @@ public sealed interface Result<T, E> permits Result.Success, Result.Error {
         }
 
         @Override
-        public @NotNull Optional<E> getOptionalError() {
+        public Optional<E> getOptionalError() {
             return Optional.empty();
         }
 
@@ -90,17 +89,17 @@ public sealed interface Result<T, E> permits Result.Success, Result.Error {
         }
 
         @Override
-        public @NotNull Optional<T> getOptional() {
+        public Optional<T> getOptional() {
             return Optional.ofNullable(result);
         }
 
         @Override
-        public void ifSuccess(@NotNull Consumer<T> handler) {
+        public void ifSuccess(Consumer<T> handler) {
             handler.accept(result);
         }
 
         @Override
-        public void ifError(@NotNull Consumer<Error<T, E>> handler) {
+        public void ifError(Consumer<Error<T, E>> handler) {
 
         }
 
@@ -143,22 +142,22 @@ public sealed interface Result<T, E> permits Result.Success, Result.Error {
         }
 
         @Override
-        public @NotNull Optional<T> getOptional() {
+        public Optional<T> getOptional() {
             return Optional.empty();
         }
 
         @Override
-        public @NotNull Optional<E> getOptionalError() {
+        public Optional<E> getOptionalError() {
             return Optional.ofNullable(message);
         }
 
         @Override
-        public void ifSuccess(@NotNull Consumer<T> handler) {
+        public void ifSuccess(Consumer<T> handler) {
 
         }
 
         @Override
-        public void ifError(@NotNull Consumer<Error<T, E>> handler) {
+        public void ifError(Consumer<Error<T, E>> handler) {
             handler.accept(this);
         }
 

src/main/java/io/github/skippyall/minions/gui/input/TextInput.kt

@@ -9,7 +9,7 @@ import net.minecraft.world.inventory.AnvilMenu
 import net.minecraft.world.item.Items
 import java.util.concurrent.CompletableFuture
 
-class TextInput<T>(
+class TextInput<T : Any>(
     parent: MinionsGui,
     val title: Component,
     val defaultValue: String,
@@ -78,7 +78,7 @@ class TextInput<T>(
 
     companion object {
         @JvmStatic
-        fun <T>input(
+        fun <T : Any>input(
             gui: MinionsGui,
             title: Component,
             defaultValue: String,
@@ -104,7 +104,7 @@ class TextInput<T>(
                 gui = gui,
                 title = title,
                 defaultValue = defaultValue,
-                parser = { result: String? -> Result.Success<String, Component>(result) },
+                parser = { result -> Result.Success(result) },
             )
         }
 
@@ -121,7 +121,7 @@ class TextInput<T>(
                 parser = { string ->
                     Result.wrapCustomError<Long, Component>(
                         { string.toLong() },
-                        Component.translatable("minions.command.input.int.fail")
+                        Component.translatable("value_type.minions.long.not_long")
                     )
                 },
             )
@@ -140,7 +140,7 @@ class TextInput<T>(
                 parser = { string ->
                     Result.wrapCustomError<Double, Component>(
                         { string.toDouble() },
-                        Component.translatable("minions.command.input.int.fail")
+                        Component.translatable("value_type.minions.long.not_long")
                     )
                 },
             )

src/main/java/io/github/skippyall/minions/gui/input/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package io.github.skippyall.minions.gui.input;
+
+import org.jspecify.annotations.NullMarked;

src/main/java/io/github/skippyall/minions/gui/instruction/ArgumentGui.java

@@ -18,7 +18,7 @@ import net.minecraft.network.chat.Component;
 import net.minecraft.world.inventory.MenuType;
 import net.minecraft.world.item.ItemStack;
 import net.minecraft.world.item.Items;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.Nullable;
 
 public class ArgumentGui extends MinionsGui {
     private final GuiContext.ValueSupplier context;
@@ -28,7 +28,7 @@ public class ArgumentGui extends MinionsGui {
     private SimpleGui gui;
 
     private @Nullable ValueSupplierType<MinionRuntime> argumentType;
-    private @Nullable ValueSupplierList.ValueSupplierEntry<?, MinionRuntime> entry;
+    private ValueSupplierList. @Nullable ValueSupplierEntry<?, MinionRuntime> entry;
 
     public ArgumentGui(MinionsGui parent, GuiContext.ValueSupplier context) {
         super(parent);
@@ -37,9 +37,7 @@ public class ArgumentGui extends MinionsGui {
         this.context = context;
 
         this.entry = instruction.getArguments().getEntry(parameter);
-        if(entry != null) {
-            this.argumentType = entry.getSupplier().getType();
-        }
+        this.argumentType = entry.getSupplier().getType();
         open();
     }
 

src/main/java/io/github/skippyall/minions/gui/instruction/ConfigureInstructionGui.java

@@ -19,6 +19,8 @@ import net.minecraft.sounds.SoundSource;
 import net.minecraft.world.inventory.MenuType;
 import net.minecraft.world.item.Items;
 
+import java.util.List;
+
 public class ConfigureInstructionGui extends MinionsGui implements ConfiguredInstructionListener, MinionListener {
     private String name;
     private final ConfiguredInstruction<MinionRuntime> instruction;
@@ -53,7 +55,9 @@ public class ConfigureInstructionGui extends MinionsGui implements ConfiguredIns
         gui.setSlot(6, new GuiElementBuilder(Items.ANVIL)
                 .setName(Component.translatable("minions.gui.instruction.configure.rename"))
                 .setCallback(() -> InstructionGui.inputInstructionName(this, context, name).thenAccept(newName -> {
-                    minion.getInstructionManager().setInstructionName(name, newName);
+                    if(newName != null) {
+                        minion.getInstructionManager().setInstructionName(name, newName);
+                    }
                     reopen();
                 }))
         );
@@ -84,6 +88,7 @@ public class ConfigureInstructionGui extends MinionsGui implements ConfiguredIns
                 })
         );
 
+        updateLastError();
         updateRunSlot();
         gui.open();
     }
@@ -105,6 +110,7 @@ public class ConfigureInstructionGui extends MinionsGui implements ConfiguredIns
     @Override
     public void onRun(ConfiguredInstruction<?> instruction) {
         updateRunSlot();
+        updateLastError();
     }
 
     @Override
@@ -131,6 +137,18 @@ public class ConfigureInstructionGui extends MinionsGui implements ConfiguredIns
         }
     }
 
+    private void updateLastError() {
+        List<Component> errors = instruction.getLastErrors();
+        if(!errors.isEmpty()) {
+            GuiElementBuilder builder = new GuiElementBuilder(Items.RED_WOOL)
+                    .setName(Component.translatable("minions.gui.instruction.last_errors"));
+            for(Component error : errors) {
+                builder.addLoreLine(error);
+            }
+            gui.setSlot(17, builder);
+        }
+    }
+
     private void updateSuppliers() {
         int slot = 12;
         for(Parameter<?> parameter : instruction.getInstruction().getParameters().reversed()) {

src/main/java/io/github/skippyall/minions/gui/instruction/ConverterGui.java

@@ -14,7 +14,7 @@ import net.minecraft.core.RegistryAccess;
 import net.minecraft.network.chat.Component;
 import net.minecraft.world.inventory.MenuType;
 import net.minecraft.world.item.Items;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.Nullable;
 
 public class ConverterGui extends MinionsGui {
     private @Nullable ValueConverterType<?> valueConverterType;

src/main/java/io/github/skippyall/minions/gui/instruction/ConverterListGui.java

@@ -12,6 +12,7 @@ import io.github.skippyall.minions.util.TranslationUtil;
 import net.minecraft.network.chat.Component;
 import net.minecraft.world.inventory.MenuType;
 import net.minecraft.world.item.Items;
+import org.jspecify.annotations.Nullable;
 
 public class ConverterListGui extends MinionsGui {
     private ConverterList converters;
@@ -61,53 +62,117 @@ public class ConverterListGui extends MinionsGui {
                 })
         );
 
-        gui.setSlot(8, backButton());
+        gui.setSlot(26, backButton());
 
         gui.open();
     }
 
+    private ValueType<?> getInputTypeOfConverter(int converterIndex) {
+        if(converterIndex < converters.getConverters().size() && converterIndex >= 0) {
+            return converters.getConverters().get(converterIndex).getFrom();
+        } else if(converterIndex == converters.getConverters().size()) {
+            return outputType;
+        } else {
+            throw new IndexOutOfBoundsException("Can't get input type of converter " + converterIndex + ", list size " + converters.getConverters().size());
+        }
+    }
+
+    private ValueType<?> getOutputTypeOfConverter(int converterIndex) {
+        if(converterIndex < converters.getConverters().size() && converterIndex >= 0) {
+            return converters.getConverters().get(converterIndex).getTo();
+        } else if(converterIndex == -1) {
+            return inputType;
+        } else {
+            throw new IndexOutOfBoundsException("Can't get output type of converter " + converterIndex + ", list size " + converters.getConverters().size());
+        }
+    }
+
     public void updateConverters() {
-        for(int slot = 9; slot < 18; slot++) {
+        for(int slot = 0; slot < 18; slot++) {
             gui.clearSlot(slot);
         }
 
         int lastConverter = Math.min(5, converters.getConverters().size() + 2 - page * 4);
         for(int i = 0; i < lastConverter; i++) {
             //Each page has 5 converters, but the last is displayed on the next page as well
-            int converterIndex = page * 4 + i;
-            //without input element
-            int actualConverterIndex = converterIndex - 1;
+            //The input element index is -1, the output element index is the list size
+            int converterIndex = page * 4 + i - 1;
             int slot = 9 + 2 * i;
-            if(converterIndex == 0) {
-                gui.setSlot(slot, new GuiElementBuilder(Items.DROPPER));
-            } else if(converterIndex == converters.getConverters().size() + 1) {
+
+            if(converterIndex == converters.getConverters().size()) {
                 gui.setSlot(slot, new GuiElementBuilder(Items.HOPPER));
             } else {
-                ValueConverter<?, ?> converter = converters.getConverters().get(actualConverterIndex);
-                ValueType<?> fromType = actualConverterIndex >= 1 ? converters.getConverters().get(actualConverterIndex - 1).getTo() : inputType;
-                ValueType<?> toType = actualConverterIndex < converters.getConverters().size() - 1 ? converters.getConverters().get(actualConverterIndex + 1).getFrom() : outputType;
+                ValueType<?> thisConverterOutput = getOutputTypeOfConverter(converterIndex);
+                ValueType<?> nextConverterInput = getInputTypeOfConverter(converterIndex + 1);
 
-                gui.setSlot(slot, new GuiElementBuilder(GuiDisplay.getDisplayStackWithName(MinionRegistries.VALUE_CONVERTER_TYPES, converter.getType(), viewer.registryAccess()))
-                        .addLoreLine(converter.getDisplayText())
-                        .setCallback(() -> new ConverterGui(this, converter, fromType, toType, converters, false, actualConverterIndex))
-                );
-            }
-            if(i != 4 && actualConverterIndex != converters.getConverters().size()) {
-                ValueType<?> fromType = actualConverterIndex >= 0 ? converters.getConverters().get(actualConverterIndex).getTo() : inputType;
-                ValueType<?> toType = actualConverterIndex < converters.getConverters().size() - 1 ? converters.getConverters().get(actualConverterIndex + 1).getFrom() : outputType;
+                //What should be shown at the converter's slot
+                if (converterIndex == -1) {
+                    gui.setSlot(slot, new GuiElementBuilder(Items.DROPPER));
+                } else {
+                    ValueType<?> previousConverterOutput = getOutputTypeOfConverter(converterIndex - 1);
 
-                gui.setSlot(slot + 1, new GuiElementBuilder(Items.MAGENTA_GLAZED_TERRACOTTA)
-                        .setName(Component.translatable(
-                                "minions.gui.instruction.converters.cast",
-                                Component.translatable(TranslationUtil.getTranslationKey(fromType, MinionRegistries.VALUE_TYPES)),
-                                Component.translatable(TranslationUtil.getTranslationKey(toType, MinionRegistries.VALUE_TYPES))
-                        ))
-                        .setCallback(() -> new ConverterGui(this, null, fromType, toType, converters, true, actualConverterIndex + 1))
-                );
+                    ValueConverter<?, ?> converter = converters.getConverters().get(converterIndex);
+                    gui.setSlot(slot, createConverterDisplay(converter, previousConverterOutput, nextConverterInput, converterIndex));
+
+                    GuiElementBuilder warning = createConverterWarning(converter);
+                    if (warning != null) {
+                        gui.setSlot(slot - 8, warning);
+                    }
+                }
+
+                //show cast in the next slot
+                if (i != 4 && converterIndex != converters.getConverters().size()) {
+                    gui.setSlot(slot + 1, createCastDisplay(thisConverterOutput, nextConverterInput, converterIndex + 1));
+
+                    GuiElementBuilder warning = createCastWarning(thisConverterOutput, nextConverterInput);
+                    if (warning != null) {
+                        gui.setSlot(slot - 8, warning);
+                    }
+                }
             }
         }
     }
 
+    private GuiElementBuilder createConverterDisplay(ValueConverter<?, ?> converter, ValueType<?> fromType, ValueType<?> toType, int converterIndex) {
+        return new GuiElementBuilder(GuiDisplay.getDisplayStackWithName(MinionRegistries.VALUE_CONVERTER_TYPES, converter.getType(), viewer.registryAccess()))
+                .addLoreLine(converter.getDisplayText())
+                .setCallback(() -> new ConverterGui(this, converter, fromType, toType, converters, false, converterIndex));
+    }
+
+    private GuiElementBuilder createCastDisplay(ValueType<?> fromType, ValueType<?> toType, int newConverterIndex) {
+        return new GuiElementBuilder(Items.MAGENTA_GLAZED_TERRACOTTA)
+                .setName(Component.translatable(
+                        "minions.gui.instruction.converters.cast",
+                        Component.translatable(TranslationUtil.getTranslationKey(fromType, MinionRegistries.VALUE_TYPES)),
+                        Component.translatable(TranslationUtil.getTranslationKey(toType, MinionRegistries.VALUE_TYPES))
+                ))
+                .setCallback(() -> new ConverterGui(this, null, fromType, toType, converters, true, newConverterIndex));
+    }
+
+    private @Nullable GuiElementBuilder createCastWarning(ValueType<?> fromType, ValueType<?> toType) {
+        Component warning = ConverterList.createCastWarning(fromType, toType);
+
+        if(warning != null) {
+            return new GuiElementBuilder(Items.RED_BANNER)
+                    .setName(Component.translatable("minions.generic.error"))
+                    .addLoreLine(warning);
+        } else {
+            return null;
+        }
+    }
+
+    private @Nullable GuiElementBuilder createConverterWarning(ValueConverter<?,?> converter) {
+        Component warning = ConverterList.createConverterWarning(converter);
+
+        if(warning != null) {
+            return new GuiElementBuilder(Items.RED_BANNER)
+                    .setName(Component.translatable("minions.generic.error"))
+                    .addLoreLine(warning);
+        } else {
+            return null;
+        }
+    }
+
     @Override
     protected void closeBacking() {
         gui.close();

src/main/java/io/github/skippyall/minions/gui/instruction/InstructionGui.java

@@ -24,7 +24,7 @@ import net.minecraft.server.level.ServerPlayer;
 import net.minecraft.world.inventory.MenuType;
 import net.minecraft.world.item.ItemStack;
 import net.minecraft.world.item.Items;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import java.util.NoSuchElementException;
 import java.util.concurrent.CompletableFuture;
@@ -64,7 +64,7 @@ public class InstructionGui {
         ServerPlayer viewer = parent.viewer;
         selectInstructionModuleMenu(parent, context).thenAccept(instructionType ->
                 inputInstructionName(parent, context, "Instruction").thenAccept(name -> {
-                    if (!minion.isRemoved() && !minion.hasDisconnected()) {
+                    if (!minion.isRemoved() && !minion.hasDisconnected() && name != null) {
                         ConfiguredInstruction<MinionRuntime> configuredInstruction = minion.getInstructionManager().createInstruction(name, instructionType);
                         new ConfigureInstructionGui(parent, GuiContext.Instruction.create(context, configuredInstruction, name));
                     }
@@ -72,7 +72,7 @@ public class InstructionGui {
         );
     }
 
-    public static CompletableFuture<String> inputInstructionName(MinionsGui parent, GuiContext.Minion context, String defaultValue) {
+    public static CompletableFuture<@Nullable String> inputInstructionName(MinionsGui parent, GuiContext.Minion context, String defaultValue) {
         return TextInput.input(parent, Component.translatable("minions.gui.instruction.enter_name"), defaultValue, (name, _) -> {
             if (context.getMinion().getInstructionManager().hasInstruction(name)) {
                 return new Result.Error<>(Component.translatable("minions.gui.instruction.name_already_used"));
@@ -163,7 +163,7 @@ public class InstructionGui {
         return future;
     }
 
-    public static GuiElementBuilder createInstructionElement(InstructionType<MinionRuntime> instructionType, RegistryAccess manager) {
+    public static GuiElementBuilder createInstructionElement(@Nullable InstructionType<MinionRuntime> instructionType, RegistryAccess manager) {
         GuiElementBuilder instructionBuilder;
         if (instructionType != null) {
             instructionBuilder = new GuiElementBuilder(GuiDisplay.getDisplayStackWithName(MinionRegistries.INSTRUCTION_TYPES, instructionType, manager));

src/main/java/io/github/skippyall/minions/gui/instruction/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package io.github.skippyall.minions.gui.instruction;
+
+import org.jspecify.annotations.NullMarked;

src/main/java/io/github/skippyall/minions/gui/minion/GuiContext.kt

@@ -1,6 +1,8 @@
 package io.github.skippyall.minions.gui.minion
 
-import io.github.skippyall.minions.gui.minion.GuiContextImpl.*
+import io.github.skippyall.minions.gui.minion.GuiContextImpl.InstructionImpl
+import io.github.skippyall.minions.gui.minion.GuiContextImpl.MinionImpl
+import io.github.skippyall.minions.gui.minion.GuiContextImpl.ValueSupplierImpl
 import io.github.skippyall.minions.minion.MinionRuntime
 import io.github.skippyall.minions.minion.fakeplayer.MinionFakePlayer
 import io.github.skippyall.minions.program.instruction.ConfiguredInstruction

src/main/java/io/github/skippyall/minions/gui/minion/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package io.github.skippyall.minions.gui.minion;
+
+import org.jspecify.annotations.NullMarked;

src/main/java/io/github/skippyall/minions/gui/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package io.github.skippyall.minions.gui;
+
+import org.jspecify.annotations.NullMarked;

src/main/java/io/github/skippyall/minions/listener/BlockEntityMinionListener.java

@@ -13,7 +13,7 @@ import net.minecraft.server.MinecraftServer;
 import net.minecraft.world.level.Level;
 import net.minecraft.world.level.block.entity.BlockEntity;
 import net.minecraft.world.level.block.entity.BlockEntityType;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import java.util.Optional;
 import java.util.UUID;
@@ -45,7 +45,7 @@ public abstract class BlockEntityMinionListener<E extends BlockEntity> implement
         this.minion = null;
     }
 
-    public static <T extends BlockEntityMinionListener<?>> T getListener(Level world, BlockPos pos, UUID minionUuid, Class<T> clazz) {
+    public static <T extends BlockEntityMinionListener<?>> @Nullable T getListener(Level world, BlockPos pos, @Nullable UUID minionUuid, Class<T> clazz) {
         if(minionUuid != null) {
             for (MinionListener listener : MinionPersistentState.get(world.getServer()).getMinionData(minionUuid).getListeners()) {
                 if (listener instanceof BlockEntityMinionListener<?> tl && tl.pos.equals(pos) && tl.worldKey.equals(world.dimension()) && clazz.isInstance(tl)) {

src/main/java/io/github/skippyall/minions/listener/SerializableListenerManager.kt

@@ -5,7 +5,7 @@ import com.mojang.serialization.MapCodec
 import io.github.skippyall.minions.listener.SerializableListenerManager.SerializableListener
 import net.minecraft.core.Registry
 import net.minecraft.resources.Identifier
-import java.util.Optional
+import java.util.*
 import java.util.concurrent.CopyOnWriteArraySet
 
 class SerializableListenerManager<T : SerializableListener>(

src/main/java/io/github/skippyall/minions/listener/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package io.github.skippyall.minions.listener;
+
+import org.jspecify.annotations.NullMarked;

src/main/java/io/github/skippyall/minions/minion/MinionData.kt

@@ -8,8 +8,7 @@ import io.github.skippyall.minions.registration.MinionRegistries
 import net.minecraft.core.UUIDUtil
 import net.minecraft.server.MinecraftServer
 import net.minecraft.util.ExtraCodecs
-import java.util.Optional
-import java.util.UUID
+import java.util.*
 import kotlin.properties.ReadWriteProperty
 import kotlin.reflect.KProperty
 

src/main/java/io/github/skippyall/minions/minion/MinionItem.java

@@ -7,7 +7,6 @@ import io.github.skippyall.minions.registration.MinionComponentTypes;
 import net.fabricmc.fabric.api.networking.v1.context.PacketContext;
 import net.minecraft.core.HolderLookup;
 import net.minecraft.core.component.DataComponents;
-import net.minecraft.network.chat.Component;
 import net.minecraft.resources.Identifier;
 import net.minecraft.server.MinecraftServer;
 import net.minecraft.server.level.ServerLevel;
@@ -19,13 +18,10 @@ import net.minecraft.world.item.Item;
 import net.minecraft.world.item.ItemStack;
 import net.minecraft.world.item.Items;
 import net.minecraft.world.item.TooltipFlag;
-import net.minecraft.world.item.component.TooltipDisplay;
 import net.minecraft.world.item.context.UseOnContext;
 import net.minecraft.world.level.Level;
 import net.minecraft.world.phys.Vec2;
-import org.jetbrains.annotations.Nullable;
-
-import java.util.function.Consumer;
+import org.jspecify.annotations.Nullable;
 
 public class MinionItem extends Item implements PolymerItem {
     public MinionItem(Properties settings) {
@@ -49,13 +45,13 @@ public class MinionItem extends Item implements PolymerItem {
         return out;
     }
 
-    @Override
+    /*@Override
     public void appendHoverText(ItemStack stack, TooltipContext context, TooltipDisplay component, Consumer<Component> tooltip, TooltipFlag type) {
         //MinionData data = getData(stack);
         //if(data != null) {
         //    tooltip.accept(Component.translatable("minions.minion_item.tooltip", data.name()));
         //}
-    }
+    }*/
 
     @Override
     public InteractionResult use(Level world, Player user, InteractionHand hand) {

src/main/java/io/github/skippyall/minions/minion/MinionListener.java

@@ -3,7 +3,7 @@ package io.github.skippyall.minions.minion;
 import io.github.skippyall.minions.listener.SerializableListenerManager;
 import io.github.skippyall.minions.minion.fakeplayer.MinionFakePlayer;
 import io.github.skippyall.minions.program.instruction.ConfiguredInstruction;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.Nullable;
 
 public interface MinionListener extends SerializableListenerManager.SerializableListener {
     default void onMinionSpawn(MinionFakePlayer minion) {}

src/main/java/io/github/skippyall/minions/minion/MinionPersistentState.java

@@ -7,6 +7,8 @@ import net.minecraft.server.MinecraftServer;
 import net.minecraft.world.level.Level;
 import net.minecraft.world.level.saveddata.SavedData;
 import net.minecraft.world.level.saveddata.SavedDataType;
+import org.jspecify.annotations.Nullable;
+
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -36,7 +38,7 @@ public class MinionPersistentState extends SavedData {
         }
     }
 
-    public MinionData getMinionData(UUID uuid) {
+    public @Nullable MinionData getMinionData(UUID uuid) {
         return minionData.get(uuid);
     }
 

src/main/java/io/github/skippyall/minions/minion/MinionProfileUtils.java

@@ -8,6 +8,8 @@ import io.github.skippyall.minions.gui.input.Result;
 import net.minecraft.network.chat.Component;
 import net.minecraft.server.MinecraftServer;
 import net.minecraft.util.StringUtil;
+import org.jspecify.annotations.Nullable;
+
 import java.util.UUID;
 
 import static io.github.skippyall.minions.Minions.LOGGER;
@@ -17,7 +19,7 @@ public class MinionProfileUtils {
         return MinionsConfig.get().minion.minionPrefix;
     }
 
-    public static GameProfile makeNewMinionProfile(UUID uuidMinion, String username, PropertyMap skin) {
+    public static GameProfile makeNewMinionProfile(@Nullable UUID uuidMinion, String username, @Nullable PropertyMap skin) {
         if(uuidMinion == null) {
             uuidMinion = UUID.randomUUID();
         }

src/main/java/io/github/skippyall/minions/minion/fakeplayer/MinionFakePlayer.java

@@ -51,7 +51,7 @@ import net.minecraft.world.level.storage.ValueInput;
 import net.minecraft.world.level.storage.ValueOutput;
 import net.minecraft.world.phys.Vec2;
 import net.minecraft.world.phys.Vec3;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import java.util.Optional;
 import java.util.Set;

src/main/java/io/github/skippyall/minions/minion/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package io.github.skippyall.minions.minion;
+
+import org.jspecify.annotations.NullMarked;

src/main/java/io/github/skippyall/minions/minion/program/instruction/MineBlockExecution.java

@@ -16,9 +16,10 @@ import net.minecraft.world.level.storage.ValueInput;
 import net.minecraft.world.level.storage.ValueOutput;
 import net.minecraft.world.phys.BlockHitResult;
 import net.minecraft.world.phys.HitResult;
+import org.jspecify.annotations.Nullable;
 
 public class MineBlockExecution implements InstructionExecution<MinionRuntime> {
-    private BlockPos currentBlock;
+    private @Nullable BlockPos currentBlock;
     private float currentBlockDamage = 0;
     private boolean first = true;
     private boolean done = false;
@@ -38,7 +39,6 @@ public class MineBlockExecution implements InstructionExecution<MinionRuntime> {
             }
             if (player.blockActionRestricted(player.level(), hit.getBlockPos(), player.gameMode.getGameModeForPlayer())) {
                 done = true;
-                return;
             }
         } else {
             done = true;

src/main/java/io/github/skippyall/minions/minion/program/instruction/inventory/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package io.github.skippyall.minions.minion.program.instruction.inventory;
+
+import org.jspecify.annotations.NullMarked;

src/main/java/io/github/skippyall/minions/minion/program/instruction/move/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package io.github.skippyall.minions.minion.program.instruction.move;
+
+import org.jspecify.annotations.NullMarked;

src/main/java/io/github/skippyall/minions/minion/program/instruction/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package io.github.skippyall.minions.minion.program.instruction;
+
+import org.jspecify.annotations.NullMarked;

src/main/java/io/github/skippyall/minions/minion/program/supplier/AnalogInputSupplier.java

@@ -22,7 +22,7 @@ import net.minecraft.resources.ResourceKey;
 import net.minecraft.world.inventory.MenuType;
 import net.minecraft.world.item.ItemStack;
 import net.minecraft.world.level.Level;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import java.util.concurrent.CompletableFuture;
 

src/main/java/io/github/skippyall/minions/minion/program/supplier/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package io.github.skippyall.minions.minion.program.supplier;
+
+import org.jspecify.annotations.NullMarked;

src/main/java/io/github/skippyall/minions/minion/skin/NameSkinProvider.java

@@ -4,12 +4,13 @@ import io.github.skippyall.minions.gui.MinionsGui;
 import io.github.skippyall.minions.gui.input.TextInput;
 import net.minecraft.network.chat.Component;
 import net.minecraft.world.item.component.ResolvableProfile;
+import org.jspecify.annotations.Nullable;
 
 import java.util.concurrent.CompletableFuture;
 
 public class NameSkinProvider implements SkinProvider {
     @Override
-    public CompletableFuture<ResolvableProfile> openSkinMenu(MinionsGui parent) {
+    public CompletableFuture<@Nullable ResolvableProfile> openSkinMenu(MinionsGui parent) {
         return TextInput.inputString(parent, Component.translatable("minions.gui.look.skin.name.title"), "")
                 .thenApply(name -> name != null ? ResolvableProfile.createUnresolved(name) : null);
     }

src/main/java/io/github/skippyall/minions/minion/skin/SkinProvider.java

@@ -3,11 +3,12 @@ package io.github.skippyall.minions.minion.skin;
 import io.github.skippyall.minions.gui.MinionsGui;
 import net.minecraft.network.chat.Component;
 import net.minecraft.world.item.component.ResolvableProfile;
+import org.jspecify.annotations.Nullable;
 
 import java.util.concurrent.CompletableFuture;
 
 public interface SkinProvider {
-    CompletableFuture<ResolvableProfile> openSkinMenu(MinionsGui parent);
+    CompletableFuture<@Nullable ResolvableProfile> openSkinMenu(MinionsGui parent);
 
     Component getDisplayName();
 }

src/main/java/io/github/skippyall/minions/minion/skin/UUIDSkinProvider.java

@@ -4,12 +4,13 @@ import io.github.skippyall.minions.gui.MinionsGui;
 import io.github.skippyall.minions.gui.input.TextInput;
 import net.minecraft.network.chat.Component;
 import net.minecraft.world.item.component.ResolvableProfile;
+import org.jspecify.annotations.Nullable;
 
 import java.util.concurrent.CompletableFuture;
 
 public class UUIDSkinProvider implements SkinProvider {
     @Override
-    public CompletableFuture<ResolvableProfile> openSkinMenu(MinionsGui parent) {
+    public CompletableFuture<@Nullable ResolvableProfile> openSkinMenu(MinionsGui parent) {
         return TextInput.inputString(parent, Component.translatable("minions.gui.look.skin.uuid.title"), "")
                 .thenApply(name -> name != null ? ResolvableProfile.createUnresolved(name) : null);
     }

src/main/java/io/github/skippyall/minions/minion/skin/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package io.github.skippyall.minions.minion.skin;
+
+import org.jspecify.annotations.NullMarked;

src/main/java/io/github/skippyall/minions/mixins/EntityGetterMixin.java

@@ -3,7 +3,7 @@ package io.github.skippyall.minions.mixins;
 import io.github.skippyall.minions.mixinhelper.EntityViewMixinHelper;
 import net.minecraft.world.entity.Entity;
 import net.minecraft.world.level.EntityGetter;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.Nullable;
 import org.spongepowered.asm.mixin.Mixin;
 import org.spongepowered.asm.mixin.injection.At;
 import org.spongepowered.asm.mixin.injection.ModifyArg;

src/main/java/io/github/skippyall/minions/mixins/EntityMixin.java

@@ -4,7 +4,7 @@ import io.github.skippyall.minions.minion.fakeplayer.MinionFakePlayer;
 import net.minecraft.world.entity.Entity;
 import net.minecraft.world.entity.LivingEntity;
 import net.minecraft.world.level.Level;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.Nullable;
 import org.spongepowered.asm.mixin.Mixin;
 import org.spongepowered.asm.mixin.Shadow;
 import org.spongepowered.asm.mixin.injection.At;

src/main/java/io/github/skippyall/minions/module/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package io.github.skippyall.minions.module;
+
+import org.jspecify.annotations.NullMarked;

src/main/java/io/github/skippyall/minions/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package io.github.skippyall.minions;
+
+import org.jspecify.annotations.NullMarked;

src/main/java/io/github/skippyall/minions/polymer/VersionSync.java

@@ -8,11 +8,12 @@ import net.minecraft.network.codec.StreamCodec;
 import net.minecraft.network.protocol.common.custom.CustomPacketPayload;
 import net.minecraft.resources.Identifier;
 import net.minecraft.server.network.ServerGamePacketListenerImpl;
+import org.jspecify.annotations.Nullable;
 
 public class VersionSync {
     public static final int NETWORK_VERSION = 1;
 
-    public static boolean isOnClient(PacketContext context) {
+    public static boolean isOnClient(@Nullable PacketContext context) {
         if(context != null && context.get(PacketContext.CONNECTION).getPacketListener() instanceof ServerGamePacketListenerImpl gamePacketListener) {
             return isOnClient(gamePacketListener);
         }

src/main/java/io/github/skippyall/minions/polymer/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package io.github.skippyall.minions.polymer;
+
+import org.jspecify.annotations.NullMarked;

src/main/java/io/github/skippyall/minions/program/consumer/ValueConsumer.java

@@ -4,7 +4,7 @@ import com.mojang.serialization.Codec;
 import io.github.skippyall.minions.program.InstructionRuntime;
 import io.github.skippyall.minions.program.value.ValueType;
 import io.github.skippyall.minions.registration.MinionRegistries;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.Nullable;
 
 /**
  * An <code>ValueSupplier</code> can be supplied to an instruction with a matching parameter.

src/main/java/io/github/skippyall/minions/program/consumer/ValueConsumerList.java

@@ -3,6 +3,7 @@ package io.github.skippyall.minions.program.consumer;
 import com.mojang.serialization.Codec;
 import io.github.skippyall.minions.program.InstructionRuntime;
 import io.github.skippyall.minions.program.supplier.Parameter;
+import org.jspecify.annotations.Nullable;
 
 import java.util.ArrayList;
 import java.util.HashMap;
@@ -22,7 +23,7 @@ public class ValueConsumerList<R extends InstructionRuntime<R>> {
         this.valueConsumers = new HashMap<>(valueConsumers);
     }
 
-    public <T, A extends ValueConsumer<T,R>> A getValueConsumer(Parameter<T> parameter) {
+    public <T, A extends ValueConsumer<T,R>> @Nullable A getValueConsumer(Parameter<T> parameter) {
         ValueConsumer<?,R> argument = valueConsumers.get(parameter.name());
         return argument == null ? null : argument.cast(parameter.type());
     }

src/main/java/io/github/skippyall/minions/program/consumer/ValueConsumerType.java

@@ -4,7 +4,7 @@ import com.mojang.serialization.Codec;
 import io.github.skippyall.minions.program.InstructionRuntime;
 import io.github.skippyall.minions.program.value.ValueType;
 import net.minecraft.server.level.ServerPlayer;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import java.util.concurrent.CompletableFuture;
 

src/main/java/io/github/skippyall/minions/program/consumer/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package io.github.skippyall.minions.program.consumer;
+
+import org.jspecify.annotations.NullMarked;

src/main/java/io/github/skippyall/minions/program/conversion/CastConverter.java

@@ -10,7 +10,7 @@ import io.github.skippyall.minions.registration.MinionRegistries;
 import io.github.skippyall.minions.registration.ValueConverters;
 import io.github.skippyall.minions.util.TranslationUtil;
 import net.minecraft.network.chat.Component;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import java.util.concurrent.CompletableFuture;
 

src/main/java/io/github/skippyall/minions/program/conversion/Casts.java

@@ -7,7 +7,7 @@ import io.github.skippyall.minions.registration.MinionRegistries;
 import io.github.skippyall.minions.registration.ValueTypes;
 import io.github.skippyall.minions.util.TranslationUtil;
 import net.minecraft.network.chat.Component;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.Nullable;
 
 public class Casts {
     public static <F,T> @Nullable Cast<F,T> getCast(ValueType<F> from, ValueType<T> to) {
@@ -28,11 +28,16 @@ public class Casts {
             return (Cast<F, T>) new Cast.CastCrafter<>(from, ValueTypes.STRING, String::valueOf).craftCast();
         }
 
+        if(from == ValueTypes.STRING && to == ValueTypes.DOUBLE) {
+            //noinspection unchecked
+            return (Cast<F, T>) new Cast.CastCrafter<>(ValueTypes.STRING, ValueTypes.DOUBLE, Double::parseDouble).canFail().lossy().craftCast();
+        }
+
         return null;
     }
 
     public static <F,T> @Nullable T cast(TypedValue<F> from, ValueType<T> to) {
-        @Nullable Cast<F,T> cast = getCast(from.type(), to);
+        Cast<F,T> cast = getCast(from.type(), to);
         if(cast != null) {
             return cast.cast(from.value());
         } else {

src/main/java/io/github/skippyall/minions/program/conversion/ConverterList.java

@@ -4,8 +4,10 @@ import com.mojang.serialization.Codec;
 import io.github.skippyall.minions.gui.input.Result;
 import io.github.skippyall.minions.program.value.TypedValue;
 import io.github.skippyall.minions.program.value.ValueType;
+import io.github.skippyall.minions.registration.MinionRegistries;
+import io.github.skippyall.minions.util.TranslationUtil;
 import net.minecraft.network.chat.Component;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import java.util.ArrayList;
 import java.util.List;
@@ -64,8 +66,19 @@ public class ConverterList {
         }
     }
 
-    public Result<@Nullable Void, Component> check() {
-        return new Result.Success<>(null);
+    public static @Nullable Component createConverterWarning(ValueConverter<?, ?> converter) {
+        return null;
+    }
+
+    public static @Nullable Component createCastWarning(ValueType<?> fromType, ValueType<?> toType) {
+        Component warning = null;
+
+        Cast<?,?> cast = Casts.getCast(fromType, toType);
+        if(cast == null) {
+            warning = Component.translatable("minions.converter.cast.not_found", TranslationUtil.getTranslation(fromType, MinionRegistries.VALUE_TYPES), TranslationUtil.getTranslation(toType, MinionRegistries.VALUE_TYPES));
+        }
+
+        return warning;
     }
 
     @Override

src/main/java/io/github/skippyall/minions/program/conversion/EqualityConverter.java

@@ -8,7 +8,7 @@ import io.github.skippyall.minions.registration.MinionRegistries;
 import io.github.skippyall.minions.registration.ValueConverters;
 import io.github.skippyall.minions.registration.ValueTypes;
 import net.minecraft.network.chat.Component;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import java.util.concurrent.CompletableFuture;
 

src/main/java/io/github/skippyall/minions/program/conversion/ValueConverter.java

@@ -5,6 +5,7 @@ import io.github.skippyall.minions.gui.input.Result;
 import io.github.skippyall.minions.program.value.ValueType;
 import io.github.skippyall.minions.registration.MinionRegistries;
 import net.minecraft.network.chat.Component;
+import org.jspecify.annotations.Nullable;
 
 public interface ValueConverter<F,T> {
     Codec<ValueConverter<?,?>> CODEC = MinionRegistries.VALUE_CONVERTER_TYPES.byNameCodec().dispatch(ValueConverter::getType, ValueConverterType::getCodec);
@@ -19,7 +20,7 @@ public interface ValueConverter<F,T> {
 
     Component getDisplayText();
 
-    default <F2,T2> ValueConverter<F2,T2> cast(ValueType<F2> from, ValueType<T2> to) {
+    default <F2,T2> @Nullable ValueConverter<F2,T2> cast(ValueType<F2> from, ValueType<T2> to) {
         if(from == getFrom() && to == getTo()) {
             //noinspection unchecked
             return (ValueConverter<F2, T2>) this;

src/main/java/io/github/skippyall/minions/program/conversion/ValueConverterType.java

@@ -3,7 +3,7 @@ package io.github.skippyall.minions.program.conversion;
 import com.mojang.serialization.MapCodec;
 import io.github.skippyall.minions.gui.MinionsGui;
 import io.github.skippyall.minions.program.value.ValueType;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import java.util.concurrent.CompletableFuture;
 

src/main/java/io/github/skippyall/minions/program/conversion/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package io.github.skippyall.minions.program.conversion;
+
+import org.jspecify.annotations.NullMarked;

src/main/java/io/github/skippyall/minions/program/instruction/ConfiguredInstruction.java

@@ -8,9 +8,13 @@ import io.github.skippyall.minions.program.supplier.Parameter;
 import io.github.skippyall.minions.program.supplier.ParameterValueList;
 import io.github.skippyall.minions.program.supplier.ValueSupplierList;
 import io.github.skippyall.minions.registration.MinionRegistries;
+import net.minecraft.network.chat.Component;
 import net.minecraft.world.level.storage.ValueInput;
 import net.minecraft.world.level.storage.ValueOutput;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.Nullable;
+
+import java.util.ArrayList;
+import java.util.List;
 
 /**
  * Holds an instruction, its configuration and is responsible for executing the instruction
@@ -24,6 +28,7 @@ public class ConfiguredInstruction<R extends InstructionRuntime<R>> {
     private boolean paused = false;
 
     private SerializableListenerManager<ConfiguredInstructionListener> listeners = new SerializableListenerManager<>();
+    private List<Component> lastErrors = List.of();
 
     private ConfiguredInstruction(
             InstructionType<R> instruction,
@@ -64,8 +69,18 @@ public class ConfiguredInstruction<R extends InstructionRuntime<R>> {
         return arguments;
     }
 
+    public List<Component> preCheck() {
+        List<Component> errors = new ArrayList<>();
+        arguments.checkRun(instruction, errors::add);
+        return errors;
+    }
+
     public boolean canRun() {
-        return instruction != null && arguments != null && arguments.checkRun(instruction) == null;
+        return preCheck().isEmpty();
+    }
+
+    public List<Component> getLastErrors() {
+        return lastErrors;
     }
 
     public boolean isRunning() {
@@ -78,15 +93,21 @@ public class ConfiguredInstruction<R extends InstructionRuntime<R>> {
 
     public void run(R minion) {
         if(canRun() && !isRunning()) {
+            lastErrors = new ArrayList<>();
             try {
-                ParameterValueList resolvedArguments = arguments.resolve(minion);
-                execution = instruction.createExecution(resolvedArguments, minion);
-                execution.start(minion);
+                ParameterValueList resolvedArguments = arguments.resolve(minion, lastErrors::add);
+                if(lastErrors.isEmpty()) {
+                    execution = instruction.createExecution(resolvedArguments, minion);
+                    execution.start(minion);
+                }
             } catch (Exception e) {
                 Minions.LOGGER.error("An error occurred while executing configured Instruction", e);
+                lastErrors.add(Component.translatable("minions.gui.instruction.check.internal_error"));
             }
 
-            listeners.forEach(listener -> listener.onRun(this));
+            for(ConfiguredInstructionListener listener : listeners) {
+                listener.onRun(this);
+            }
         }
     }
 

src/main/java/io/github/skippyall/minions/program/instruction/execution/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package io.github.skippyall.minions.program.instruction.execution;
+
+import org.jspecify.annotations.NullMarked;

src/main/java/io/github/skippyall/minions/program/instruction/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package io.github.skippyall.minions.program.instruction;
+
+import org.jspecify.annotations.NullMarked;

src/main/java/io/github/skippyall/minions/program/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package io.github.skippyall.minions.program;
+
+import org.jspecify.annotations.NullMarked;

src/main/java/io/github/skippyall/minions/program/supplier/FixedValueSupplierType.java

@@ -4,7 +4,7 @@ import com.mojang.serialization.Codec;
 import io.github.skippyall.minions.gui.MinionsGui;
 import io.github.skippyall.minions.program.InstructionRuntime;
 import io.github.skippyall.minions.program.value.ValueType;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import java.util.concurrent.CompletableFuture;
 

src/main/java/io/github/skippyall/minions/program/supplier/Parameter.java

@@ -5,7 +5,7 @@ import com.mojang.serialization.MapCodec;
 import com.mojang.serialization.codecs.RecordCodecBuilder;
 import io.github.skippyall.minions.program.value.ValueType;
 import io.github.skippyall.minions.registration.MinionRegistries;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.Nullable;
 
 public record Parameter<T>(String name, ValueType<T> type) {
     public static final MapCodec<Parameter<?>> MAP_CODEC = RecordCodecBuilder.mapCodec(instance ->

src/main/java/io/github/skippyall/minions/program/supplier/ValueSupplier.java

@@ -6,7 +6,7 @@ import io.github.skippyall.minions.program.InstructionRuntime;
 import io.github.skippyall.minions.program.value.ValueType;
 import io.github.skippyall.minions.registration.MinionRegistries;
 import net.minecraft.network.chat.Component;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.Nullable;
 
 /**
  * An <code>ValueSupplier</code> can be supplied to an instruction with a matching parameter.
@@ -53,8 +53,9 @@ public interface ValueSupplier<T, R extends InstructionRuntime<R>> {
                                 "type",
                                 s -> DataResult.success(s.getValueType()),
                                 valueType -> {
-                                    if(type.getCodec(valueType) != null) {
-                                        return DataResult.success(type.getCodec(valueType).fieldOf("valueType"));
+                                    Codec<? extends ValueSupplier<?, R>> valueTypeCodec = type.getCodec(valueType);
+                                    if(valueTypeCodec != null) {
+                                        return DataResult.success(valueTypeCodec.fieldOf("valueType"));
                                     } else {
                                         return DataResult.error(() -> "Supplier type " + type + "not available for value type " + valueType);
                                     }

src/main/java/io/github/skippyall/minions/program/supplier/ValueSupplierList.java

@@ -10,7 +10,7 @@ import io.github.skippyall.minions.program.conversion.ConverterList;
 import io.github.skippyall.minions.program.instruction.InstructionType;
 import io.github.skippyall.minions.program.value.TypedValue;
 import net.minecraft.network.chat.Component;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import java.util.ArrayList;
 import java.util.Collection;
@@ -37,7 +37,7 @@ public class ValueSupplierList<R extends InstructionRuntime<R>> {
         return List.copyOf(arguments.values());
     }
 
-    public ValueSupplier<?,R> getArgument(Parameter<?> parameter) {
+    public @Nullable ValueSupplier<?,R> getArgument(Parameter<?> parameter) {
         if(arguments.containsKey(parameter)) {
             return arguments.get(parameter).supplier;
         } else {
@@ -60,10 +60,10 @@ public class ValueSupplierList<R extends InstructionRuntime<R>> {
         arguments.remove(parameter);
     }
 
-    public ParameterValueList resolve(R runtime) {
+    public ParameterValueList resolve(R runtime, Consumer<Component> errorConsumer) {
         ParameterValueList list = new ParameterValueList();
         for(ValueSupplierEntry<?,R> argument : arguments.values()) {
-            argument.addToList(list, runtime);
+            argument.addToList(list, runtime, errorConsumer);
         }
         return list;
     }
@@ -72,28 +72,20 @@ public class ValueSupplierList<R extends InstructionRuntime<R>> {
         return arguments.containsKey(parameter);
     }
 
-    public @Nullable Component checkHasArguments(Collection<Parameter<?>> checkParameters) {
+    public void checkHasArguments(Collection<Parameter<?>> checkParameters, Consumer<Component> errorConsumer) {
         for(Parameter<?> parameter : checkParameters) {
             if(!hasArgumentFor(parameter)) {
-                return Component.translatable("minions.gui.instruction.check.argument_not_set", parameter.name());
+                errorConsumer.accept(Component.translatable("minions.gui.instruction.check.argument_not_set", parameter.name()));
             }
         }
-        return null;
     }
 
-    public @Nullable Component checkRun(InstructionType<R> instructionType) {
-        @Nullable Component checkResult = checkHasArguments(instructionType.getParameters());
-        if(checkResult != null) {
-            return checkResult;
-        }
+    public void checkRun(InstructionType<R> instructionType, Consumer<Component> errorConsumer) {
+        checkHasArguments(instructionType.getParameters(), errorConsumer);
 
         for(ValueSupplierEntry<?,R> entry : arguments.values()) {
-            checkResult = entry.check();
-            if(checkResult != null) {
-                return checkResult;
-            }
+            entry.check(errorConsumer);
         }
-        return null;
     }
 
     private void onChange(Parameter<?> parameter) {
@@ -148,15 +140,13 @@ public class ValueSupplierList<R extends InstructionRuntime<R>> {
             this.supplier = supplier;
         }
 
-        private @Nullable Component addToList(ParameterValueList list, R runtime) {
+        private void addToList(ParameterValueList list, R runtime, Consumer<Component> errorConsumer) {
             Result<P, Component> result = getValue(supplier, runtime);
             switch (result) {
-                case Result.Success<P, Component> success -> {
-                    list.setValue(parameter, success.result());
-                    return null;
-                }
+                case Result.Success<P, Component> success -> list.setValue(parameter, success.result());
                 case Result.Error<P, Component> error -> {
-                    return error.message();
+                    errorConsumer.accept(Component.translatable("minions.instruction.argument.error", parameter.name()));
+                    errorConsumer.accept(error.message());
                 }
             }
         }
@@ -168,7 +158,7 @@ public class ValueSupplierList<R extends InstructionRuntime<R>> {
             return convertedResult.flatMap(convertedValue -> Casts.castOrError(convertedValue, parameter.type()));
         }
 
-        public @Nullable Component check() {
+        public @Nullable Component check(Consumer<Component> errorConsumer) {
             //TODO check it
             return null;
         }

src/main/java/io/github/skippyall/minions/program/supplier/ValueSupplierType.java

@@ -4,12 +4,12 @@ import com.mojang.serialization.Codec;
 import io.github.skippyall.minions.gui.MinionsGui;
 import io.github.skippyall.minions.program.InstructionRuntime;
 import io.github.skippyall.minions.program.value.ValueType;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import java.util.concurrent.CompletableFuture;
 
 public abstract class ValueSupplierType<R extends InstructionRuntime<R>> {
-    public abstract <T> Codec<? extends ValueSupplier<T,R>> getCodec(ValueType<T> type);
+    public abstract <T> @Nullable Codec<? extends ValueSupplier<T,R>> getCodec(ValueType<T> type);
 
     public abstract <T> CompletableFuture<? extends ValueSupplier<?,R>> openConfiguration(MinionsGui gui, ValueType<T> valueType, @Nullable ValueSupplier<?,R> previous);
 }

src/main/java/io/github/skippyall/minions/program/supplier/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package io.github.skippyall.minions.program.supplier;
+
+import org.jspecify.annotations.NullMarked;

src/main/java/io/github/skippyall/minions/program/value/TypedValue.java

@@ -1,7 +1,9 @@
 package io.github.skippyall.minions.program.value;
 
+import java.util.Objects;
+
 public record TypedValue<T>(T value, ValueType<T> type) {
     public static <T> TypedValue<T> of(Object o, ValueType<T> type) {
-        return new TypedValue<>(type.checkedCast(o), type);
+        return new TypedValue<T>(Objects.requireNonNull(type.checkedCast(o)), type);
     }
 }

src/main/java/io/github/skippyall/minions/program/value/ValueType.java

@@ -3,7 +3,7 @@ package io.github.skippyall.minions.program.value;
 import com.mojang.serialization.Codec;
 import io.github.skippyall.minions.gui.MinionsGui;
 import net.minecraft.network.chat.Component;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import java.util.concurrent.CompletableFuture;
 

src/main/java/io/github/skippyall/minions/program/value/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package io.github.skippyall.minions.program.value;
+
+import org.jspecify.annotations.NullMarked;

src/main/java/io/github/skippyall/minions/registration/MinionBlocks.java

@@ -36,6 +36,7 @@ public class MinionBlocks {
                     FabricBlockEntityTypeBuilder.create(MinionTriggerBlockEntity::new, MINION_TRIGGER_BLOCK).build()
             );
 
+
     public static final Identifier ANALOG_INPUT_BLOCK_ID = Identifier.fromNamespaceAndPath(Minions.MOD_ID, "analog_input");
     public static final AnalogInputBlock ANALOG_INPUT_BLOCK = Registry.register(
             BuiltInRegistries.BLOCK,

src/main/java/io/github/skippyall/minions/registration/MinionCreativeTab.java

@@ -7,11 +7,13 @@ import net.minecraft.network.chat.Component;
 import net.minecraft.resources.Identifier;
 import net.minecraft.world.item.CreativeModeTab;
 import net.minecraft.world.item.Item;
+import org.jspecify.annotations.Nullable;
 
 import java.util.ArrayList;
 import java.util.List;
 
 public class MinionCreativeTab {
+    @Nullable
     public static CreativeModeTab group;
 
     private static final List<Item> items = new ArrayList<>();

src/main/java/io/github/skippyall/minions/registration/MinionItems.java

@@ -1,8 +1,7 @@
 package io.github.skippyall.minions.registration;
 
-import eu.pb4.polymer.core.api.item.PolymerBlockItem;
 import eu.pb4.polymer.core.api.item.SimplePolymerItem;
-import io.github.skippyall.minions.block.miniontrigger.MinionTriggerBlockItem;
+import io.github.skippyall.minions.block.MinionsBlockItem;
 import io.github.skippyall.minions.clipboard.ClipboardItem;
 import io.github.skippyall.minions.minion.MinionItem;
 import io.github.skippyall.minions.minion.MinionRuntime;
@@ -69,12 +68,17 @@ public class MinionItems {
             List.of(SpecialAbilities.MOB_SPAWNING)
     );
 
-    public static final PolymerBlockItem MINION_TRIGGER_ITEM =
-            registerItem(
-                    MinionBlocks.MINION_TRIGGER_ID,
-                    settings -> new MinionTriggerBlockItem(MinionBlocks.MINION_TRIGGER_BLOCK, settings, Items.COMPARATOR),
-                    new Item.Properties().useBlockDescriptionPrefix()
-            );
+    public static final MinionsBlockItem MINION_TRIGGER_ITEM = registerItem(
+            MinionBlocks.MINION_TRIGGER_ID,
+            settings -> new MinionsBlockItem(MinionBlocks.MINION_TRIGGER_BLOCK, settings, Items.COMPARATOR),
+            new Item.Properties().useBlockDescriptionPrefix()
+    );
+
+    public static final MinionsBlockItem ANALOG_INPUT_ITEM = registerItem(
+            MinionBlocks.ANALOG_INPUT_BLOCK_ID,
+            settings -> new MinionsBlockItem(MinionBlocks.ANALOG_INPUT_BLOCK, settings, Items.REPEATER),
+            new Item.Properties().useBlockDescriptionPrefix()
+    );
 
     public static final ClipboardItem REFERENCE_ITEM = registerItem(Identifier.fromNamespaceAndPath(MOD_ID, "clipboard"), ClipboardItem::new);
 

src/main/java/io/github/skippyall/minions/registration/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package io.github.skippyall.minions.registration;
+
+import org.jspecify.annotations.NullMarked;

src/main/java/io/github/skippyall/minions/util/TranslationUtil.java

@@ -1,14 +1,16 @@
 package io.github.skippyall.minions.util;
 
 import net.minecraft.core.Registry;
+import net.minecraft.network.chat.Component;
 import net.minecraft.resources.Identifier;
+import org.jspecify.annotations.Nullable;
 
 public class TranslationUtil {
-    public static <T> String getTranslationKey(T object, Registry<T> registry, String defaultKey) {
+    public static <T> String getTranslationKey(@Nullable T object, Registry<T> registry, String defaultKey) {
         return getTranslationKey(object, registry, registry.key().identifier().getPath(), defaultKey);
     }
 
-    public static <T> String getTranslationKey(T object, Registry<T> registry, String prefix, String defaultKey) {
+    public static <T> String getTranslationKey(@Nullable T object, Registry<T> registry, String prefix, String defaultKey) {
         if(object == null) {
             return defaultKey;
         }
@@ -20,7 +22,11 @@ public class TranslationUtil {
         return id.toLanguageKey(prefix);
     }
 
-    public static <T> String getTranslationKey(T object, Registry<T> registry) {
+    public static <T> String getTranslationKey(@Nullable T object, Registry<T> registry) {
         return getTranslationKey(object, registry, "minions.generic.unknown");
     }
+
+    public static <T> Component getTranslation(@Nullable T object, Registry<T> registry) {
+        return Component.translatable(TranslationUtil.getTranslationKey(object, registry));
+    }
 }

src/main/java/io/github/skippyall/minions/util/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package io.github.skippyall.minions.util;
+
+import org.jspecify.annotations.NullMarked;

src/main/resources/assets/minions/lang/en_us.json

@@ -34,6 +34,7 @@
   "minions.gui.instruction.configure.delete.confirm": "Delete %s?",
   "minions.gui.instruction.configure.copy": "Copy Reference",
   "minions.gui.instruction.configure.copy.description": "Click here and then use a Minion Trigger Block to bind it",
+  "minions.gui.instruction.last_errors": "Last Errors",
   "minions.gui.instruction.run": "Run",
   "minions.gui.instruction.stop": "Stop",
   "minions.gui.instruction.argument.title": "Argument for %s (%s)",
@@ -44,30 +45,19 @@
   "minions.gui.instruction.parameter": "%s: %s",
   "minions.gui.instruction.argument": "Argument: %s",
 
-  "minions.gui.instruction.check.argument_not_set": "Argument %s is not set",
-
   "minions.gui.instruction.converters": "Converters",
   "minions.gui.instruction.converters.cast": "Cast from %s to %s",
   "minions.gui.instruction.converter.title": "Configure Converter",
   "minions.gui.instruction.converter.type.title": "Select a Converter Type",
   "minions.gui.instruction.converter.data": "Converter Data",
 
-  "minions.converter.list.passing_error": "Error while passing previous value to converter #%s: %s",
-
-  "minions.command.input.int.fail": "Not an integer",
-  "minions.command.input.float.fail": "Not a number",
-  "minions.command.action.details": "Set how to %s",
-  "minions.command.action.once": "%s once",
-  "minions.command.action.continuous": "%s continuously",
-  "minions.command.action.interval": "%s every x seconds",
-  "minions.command.action.stop": "Stop %s",
-  "minions.command.action.interval.enter": "Enter an interval in seconds",
-  "minions.command.interact.name": "Interact",
-  "minions.command.interact.description": "Use and place blocks",
-  "minions.command.attack.name": "Attack",
-  "minions.command.attack.description": "Attack and mine blocks",
-
-  "minions.command.minion.not_present": "This minion does not exist",
+  "minions.gui.instruction.check.instruction_type_not_set": "Instruction Type is not set",
+  "minions.gui.instruction.check.arguments_not_set": "Arguments are not set",
+  "minions.gui.instruction.check.argument_not_set": "Argument %s is not set",
+  "minions.gui.instruction.check.internal_error": "Internal Error, check server console",
+  "minions.instruction.argument.error": "Error while getting argument for %s:",
+  "minions.converter.list.passing_error": "Error while passing previous value to converter #%s:",
+  "minions.converter.cast.not_found": "No cast from %s to %s",
 
   "minions.reference.instruction.tooltip": "Linked to instruction %s in %s",
   "minions.reference.block.tooltip": "Linked to block at %s",
@@ -88,6 +78,7 @@
   "instruction.minions.turn_vector.description": "Turn the head so that it faces a block with specific cardinal offsets",
 
   "value_type.minions.long": "Integer",
+  "value_type.minions.long.not_long": "Not an Integer",
   "value_type.minions.double": "Decimal",
   "value_type.minions.boolean": "Boolean",
   "value_type.minions.boolean.true": "True",
@@ -125,5 +116,6 @@
   "minions.generic.name.invalid": "Name is invalid",
   "minions.generic.name.taken": "This name is already used",
   "minions.generic.mod_name": "Minions",
-  "minions.generic.unknown": "Unknown"
+  "minions.generic.unknown": "Unknown",
+  "minions.generic.error": "Error"
 }