Fix NPE when rendering turtle's label

Minecraft.hitResult may /technically/ be null when rendering a turtle.
In vanilla, this doesn't appear to happen, but other mods (e.g.
Immersive Portals) may still take advantage of this.

This hitResult is then propagated to BlockEntityRenderDispatcher, where
the field was /not/ marked as nullable. This meant we didn't even notice
the potential of an NPE!

Closes #1775

projects/common/src/client/java/dan200/computercraft/client/render/TurtleBlockEntityRenderer.java

@@ -55,7 +55,7 @@ public void render(TurtleBlockEntity turtle, float partialTicks, PoseStack trans
         // Render the label
         var label = turtle.getLabel();
         var hit = renderer.cameraHitResult;
-        if (label != null && hit.getType() == HitResult.Type.BLOCK && turtle.getBlockPos().equals(((BlockHitResult) hit).getBlockPos())) {
+        if (label != null && hit != null && hit.getType() == HitResult.Type.BLOCK && turtle.getBlockPos().equals(((BlockHitResult) hit).getBlockPos())) {
             var mc = Minecraft.getInstance();
             var font = this.font;
 

projects/lints/src/main/kotlin/cc/tweaked/linter/MinecraftLibraryModel.kt

@@ -7,6 +7,7 @@ package cc.tweaked.linter
 import com.google.common.collect.ImmutableSet
 import com.google.common.collect.ImmutableSetMultimap
 import com.uber.nullaway.LibraryModels
+import com.uber.nullaway.LibraryModels.FieldRef.fieldRef
 import com.uber.nullaway.LibraryModels.MethodRef.methodRef
 
 /**
@@ -34,4 +35,9 @@ class MinecraftLibraryModel : LibraryModels {
         // Reasoning about nullability of BlockEntity.getLevel() is awkward. For now, assume it's non-null.
         methodRef("net.minecraft.world.level.block.entity.BlockEntity", "getLevel()"),
     )
+
+    override fun nullableFields(): ImmutableSet<LibraryModels.FieldRef> = ImmutableSet.of(
+        // This inherits from Minecraft.hitResult, and so can also be null.
+        fieldRef("net.minecraft.client.renderer.blockentity.BlockEntityRenderDispatcher", "cameraHitResult"),
+    )
 }