I'm trying to create my own custom structure. I found an example structure to reference from but I'm new to Java as a whole so I'm stuck on how to fix this.

 

Here's my code:

public void commonSetup(FMLCommonSetupEvent args) {
    DeferredWorkQueue.runLater(() -> {
        Iterator<Biome> biomes = ForgeRegistries.BIOMES.iterator();
        biomes.forEachRemaining((biome) -> {
            biome.addStructure(JUNGLE_RUIN.withConfiguration(IFeatureConfig.NO_FEATURE_CONFIG));
            biome.addFeature(GenerationStage.Decoration.SURFACE_STRUCTURES, JUNGLE_RUIN.withConfiguration(IFeatureConfig.NO_FEATURE_CONFIG).withPlacement(Placement.NOPE.configure(IPlacementConfig.NO_PLACEMENT_CONFIG)));
        });
    });
}

 

Here's the error message I got:

[18:22:01] [Render thread/ERROR] [ne.mi.fm.DeferredWorkQueue/]: Encountered exception executing deferred work
java.util.concurrent.CompletionException: java.lang.NullPointerException
	at java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:273) ~[?:1.8.0_201] {}
	at java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:280) ~[?:1.8.0_201] {}
	at java.util.concurrent.CompletableFuture$AsyncRun.run(CompletableFuture.java:1629) ~[?:1.8.0_201] {}
	at net.minecraftforge.fml.DeferredWorkQueue.lambda$makeRunnable$6(DeferredWorkQueue.java:210) ~[forge-1.15.2-31.2.0_mapped_snapshot_20200514-1.15.1-recomp.jar:?] {re:classloading}
	at java.util.concurrent.CompletableFuture$AsyncRun.run(CompletableFuture.java:1626) ~[?:1.8.0_201] {}
	at net.minecraft.resources.AsyncReloader.lambda$null$3(AsyncReloader.java:66) ~[forge-1.15.2-31.2.0_mapped_snapshot_20200514-1.15.1-recomp.jar:?] {re:classloading}
	at net.minecraft.util.concurrent.ThreadTaskExecutor.run(ThreadTaskExecutor.java:140) ~[forge-1.15.2-31.2.0_mapped_snapshot_20200514-1.15.1-recomp.jar:?] {re:classloading,pl:accesstransformer:B}
	at net.minecraft.util.concurrent.RecursiveEventLoop.run(RecursiveEventLoop.java:22) ~[forge-1.15.2-31.2.0_mapped_snapshot_20200514-1.15.1-recomp.jar:?] {re:classloading}
	at net.minecraft.util.concurrent.ThreadTaskExecutor.driveOne(ThreadTaskExecutor.java:110) ~[forge-1.15.2-31.2.0_mapped_snapshot_20200514-1.15.1-recomp.jar:?] {re:classloading,pl:accesstransformer:B}
	at net.minecraft.util.concurrent.ThreadTaskExecutor.drainTasks(ThreadTaskExecutor.java:97) ~[forge-1.15.2-31.2.0_mapped_snapshot_20200514-1.15.1-recomp.jar:?] {re:classloading,pl:accesstransformer:B}
	at net.minecraft.client.Minecraft.runGameLoop(Minecraft.java:934) ~[forge-1.15.2-31.2.0_mapped_snapshot_20200514-1.15.1-recomp.jar:?] {re:classloading,pl:accesstransformer:B,pl:runtimedistcleaner:A}
	at net.minecraft.client.Minecraft.run(Minecraft.java:558) ~[forge-1.15.2-31.2.0_mapped_snapshot_20200514-1.15.1-recomp.jar:?] {re:classloading,pl:accesstransformer:B,pl:runtimedistcleaner:A}
	at net.minecraft.client.main.Main.main(Main.java:177) ~[forge-1.15.2-31.2.0_mapped_snapshot_20200514-1.15.1-recomp.jar:?] {re:classloading,pl:runtimedistcleaner:A}
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_201] {}
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_201] {}
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_201] {}
	at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_201] {}
	at net.minecraftforge.userdev.FMLUserdevClientLaunchProvider.lambda$launchService$0(FMLUserdevClientLaunchProvider.java:55) ~[forge-1.15.2-31.2.0_mapped_snapshot_20200514-1.15.1-recomp.jar:?] {}
	at cpw.mods.modlauncher.LaunchServiceHandlerDecorator.launch(LaunchServiceHandlerDecorator.java:37) [modlauncher-5.1.0.jar:?] {}
	at cpw.mods.modlauncher.LaunchServiceHandler.launch(LaunchServiceHandler.java:54) [modlauncher-5.1.0.jar:?] {}
	at cpw.mods.modlauncher.LaunchServiceHandler.launch(LaunchServiceHandler.java:72) [modlauncher-5.1.0.jar:?] {}
	at cpw.mods.modlauncher.Launcher.run(Launcher.java:81) [modlauncher-5.1.0.jar:?] {}
	at cpw.mods.modlauncher.Launcher.main(Launcher.java:65) [modlauncher-5.1.0.jar:?] {}
	at net.minecraftforge.userdev.LaunchTesting.main(LaunchTesting.java:102) [forge-1.15.2-31.2.0_mapped_snapshot_20200514-1.15.1-recomp.jar:?] {}
Caused by: java.lang.NullPointerException
	at com.jaceg.tutorialmod.TutorialMod.lambda$null$1(TutorialMod.java:131) ~[?:?] {re:classloading}
	at java.util.Iterator.forEachRemaining(Iterator.java:116) ~[?:1.8.0_201] {}
	at com.jaceg.tutorialmod.TutorialMod.lambda$commonSetup$2(TutorialMod.java:130) ~[?:?] {re:classloading}
	at java.util.concurrent.CompletableFuture$AsyncRun.run(CompletableFuture.java:1626) ~[?:1.8.0_201] {}
	... 21 more
[18:22:01] [Server-Worker-1/INFO] [ne.mi.fm.DeferredWorkQueue/LOADING]: Synchronous work queue completed in 00:00:00.101
[18:22:01] [Server-Worker-1/FATAL] [ne.mi.fm.ModLoader/LOADING]: Failed to complete lifecycle event SETUP, 1 errors found
[18:22:01] [Server-Worker-1/FATAL] [ne.mi.ev.EventBus/EVENTBUS]: EventBus 0 shutting down - future events will not be posted.
java.lang.Exception: stacktrace
	at net.minecraftforge.eventbus.EventBus.shutdown(EventBus.java:278) ~[eventbus-2.2.0-service.jar:?] {}
	at net.minecraftforge.fml.client.ClientModLoader.lambda$createRunnableWithCatch$5(ClientModLoader.java:115) ~[?:?] {re:classloading,pl:runtimedistcleaner:A}
	at net.minecraftforge.fml.client.ClientModLoader.startModLoading(ClientModLoader.java:123) ~[?:?] {re:classloading,pl:runtimedistcleaner:A}
	at net.minecraftforge.fml.client.ClientModLoader.lambda$onreload$3(ClientModLoader.java:105) ~[?:?] {re:classloading,pl:runtimedistcleaner:A}
	at net.minecraftforge.fml.client.ClientModLoader.lambda$createRunnableWithCatch$5(ClientModLoader.java:113) ~[?:?] {re:classloading,pl:runtimedistcleaner:A}
	at java.util.concurrent.CompletableFuture$AsyncRun.run(CompletableFuture.java:1626) [?:1.8.0_201] {}
	at java.util.concurrent.CompletableFuture$AsyncRun.exec(CompletableFuture.java:1618) [?:1.8.0_201] {}
	at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289) [?:1.8.0_201] {}
	at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1056) [?:1.8.0_201] {}
	at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1692) [?:1.8.0_201] {}
	at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:157) [?:1.8.0_201] {}

 

I'm not sure what other parts of my code I need to show to get proper help but any advice would be appreciated. A link to some sort of explanation on how to add custom structures in 1.15.2 would be nice as well.

NullPointerExceptions mean that you're trying to use a property (variable) that hasn't been set. In other words, you have a variable that's empty.

 

I've been experimenting with structure gen and have gotten structure generation working, I made a thread on this page and the source is there if you need something working as a reference. I wouldn't say its particularly elegant code but it works.