java.lang.NullPointerException: Unexpected error
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By Orichalcum · Posted
I know that this may be a basic question, but I am very new to modding. I am trying to have it so that I can create modified Vanilla loot tables that use a custom enchantment as a condition (i.e. enchantment present = item). However, I am having trouble trying to implement this; the LootItemRandomChanceWithEnchantedBonusCondition constructor needs a Holder<Enchantment> and I am unable to use the getOrThrow() method on the custom enchantment declared in my mod's enchantments class. Here is what I have so far in the GLM: protected void start(HolderLookup.Provider registries) { HolderLookup.RegistryLookup<Enchantment> registrylookup = registries.lookupOrThrow(Registries.ENCHANTMENT); LootItemRandomChanceWithEnchantedBonusCondition lootItemRandomChanceWithEnchantedBonusCondition = new LootItemRandomChanceWithEnchantedBonusCondition(0.0f, LevelBasedValue.perLevel(0.07f), registrylookup.getOrThrow(*enchantment here*)); this.add("nebu_from_deepslate", new AddItemModifier(new LootItemCondition[]{ LootItemBlockStatePropertyCondition.hasBlockStateProperties(Blocks.DEEPSLATE).build(), LootItemRandomChanceCondition.randomChance(0.25f).build(), lootItemRandomChanceWithEnchantedBonusCondition }, OrichalcumItems.NEBU.get())); } Inserting Enchantments.[vanilla enchantment here] actually works but trying to declare an enchantment from my custom enchantments class as [mod enchantment class].[custom enchantment] does not work even though they are both a ResourceKey and are registered in Registries.ENCHANTMENT. Basically, how would I go about making it so that a custom enchantment declared as a ResourceKey<Enchantment> of value ResourceKey.create(Registries.ENCHANTMENT, ResourceLocation.fromNamespaceAndPath([modid], [name])), declared in a seperate enchantments class, can be used in the LootItemRandomChanceWithEnchantedBonusCondition constructor as a Holder? I can't use getOrThrow() because there is no level or block entity/entity in the start() method and it is running as datagen. It's driving me nuts. -
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By socrates3992 · Posted
Hi here is an update. I was able to fix the code so my mod does not crash Minecraft. Please understand that I am new to modding but I honestly am having a hard time understanding how anyone can get this to work without having extensive programming and debugging experience as well as searching across the Internet, multiple gen AI bots (claude, grok, openai), and examining source code hidden in the gradle directory and in various github repositories. I guess I am wrong because clearly there are thousands of mods so maybe I am just a newbie. Ok, rant over, here is a step by step summary so others can save the 3 days it took me to figure this out. 1. First, I am using forge 54.1.0 and Minecraft 1.21.4 2. I am creating a mod to add a shotgun to Minecraft 3. After creating the mod and compiling it, I installed the .jar file to the proper directory in Minecraft and used 1.21.4-forge-54.1.0 4. The mod immediately crashed with the error: Caused by: java.lang.NullPointerException: Item id not set 5. Using the stack trace, I determined that the Exception was being thrown from the net.minecraft.world.item.Item.Properties class 6. It seems that there are no javadocs for this class, so I used IntelliJ which was able to provide a decompiled version of the class, which I then examined to see the source of the error. Side question: Are there javadocs? 7. This method, specifically, was the culprit: protected String effectiveDescriptionId() { return this.descriptionId.get(Objects.requireNonNull(this.id, "Item id not set")); } 8. Now my quest was to determine how to set this.id. Looking at the same source file, I determined there was another method: public Item.Properties setId(ResourceKey<Item> pId) { this.id = pId; return this; } 9. So now, I need to figure out how to call setId(). This required working backwards a bit. Starting from the constructor, I stubbed out the variable p which is of type Item.Properties public static final RegistryObject<Item> SHOTGUN = ITEMS.register("shotgun", () -> new ShotgunItem(p)); Rather than putting this all on one line, I split it up for readability like this: private static final Item.Properties p = new Item.Properties().useItemDescriptionPrefix().setId(rk); Here is was the missing function, setId(), which takes a type of ResourceKey<Item>. My next problem is that due to the apparent lack of documentation (I tried searching the docs on this site) I could not determine the full import path to ResourceKey. I did some random searching on the Internet and stumbled across a Github repository which gave two clues: import net.minecraft.resources.ResourceKey; import net.minecraft.resources.ResourceLocation; Then I created the rk variable like this: private static ResourceKey<Item> rk = ResourceKey.create(Registries.ITEM, ResourceLocation.parse("modid:shotgunmod")); And now putting it all together in order: private static ResourceKey<Item> rk = ResourceKey.create(Registries.ITEM, ResourceLocation.parse("modid:shotgunmod")); private static final Item.Properties p = new Item.Properties().useItemDescriptionPrefix().setId(rk); public static final RegistryObject<Item> SHOTGUN = ITEMS.register("shotgun", () -> new ShotgunItem(p)); This compiled and the mod no longer crashes. I still have more to do on it, but hopefully this will save someone hours. I welcome any feedback and if I missed some obvious modding resource or tutorial that has this information. If not, I might suggest we add it somewhere for people trying to write a mod that doesn't crash. Thank you !!! -
By socrates3992 · Posted
I will keep adding to this thread with more information in case anyone can help, or at the very least I can keep my troubleshooting organized. I decided to downgrade to 54.1.0 in the hopes that this would fix the issue but it didn't. At least now I am on a "recommended" version. The crash report did confirm my earlier post that the Exception is coming from effectiveDescriptionId(). I'll continue to see if I can find a way to set the ID manually. Caused by: java.lang.NullPointerException: Item id not set at java.base/java.util.Objects.requireNonNull(Objects.java:259) ~[?:?] at TRANSFORMER/[email protected]/net.minecraft.world.item.Item$Properties.effectiveDescriptionId(Item.java:465) ~[forge-1.21.4-54.1.0-client.jar!/:?] at TRANSFORMER/[email protected]/net.minecraft.world.item.Item.<init>(Item.java:111) ~[forge-1.21.4-54.1.0-client.jar!/:?] at TRANSFORMER/[email protected]/com.example.shotgunmod.ShotgunItem.<init>(ShotgunItem.java:19) ~[shotgunmod-1.0.0.jar!/:1.0.0] at TRANSFORMER/[email protected]/com.example.shotgunmod.ModItems.lambda$static$0(ModItems.java:15) ~[shotgunmod-1.0.0.jar!/:1.0.0] at TRANSFORMER/[email protected]/net.minecraftforge.registries.DeferredRegister$EventDispatcher.lambda$handleEvent -
It just randomly stop working after a rebooted my dedicated server PLEASE HELP! com.google.gson Failed to start the minecraft server com.google.gson.JsonSyntaxException: Expected a com.google.gson.JsonObject but was com.google.gson.JsonPrimitive; at path $
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