Describe what you were doing before the crash
Flying around the world, just generally testing the mod.

To Reproduce
Steps to reproduce the behavior (if possible):

1. Create a world
2. Fly around through as many biomes as possible
3. Wait for crash

Crash Log (REQUIRED)
`---- Minecraft Crash Report ----
// Don't do that.

Time: 16/07/20 6:00 PM
Description: Exception generating new chunk

java.lang.NullPointerException: Exception generating new chunk
at net.minecraft.nbt.StringNBT.func_229705_a_(StringNBT.java:40) ~[?:?] {re:classloading}
at net.minecraft.nbt.CompoundNBT.func_74778_a(CompoundNBT.java:150) ~[?:?] {re:classloading}
at dev.itsmeow.betteranimalsplus.imdlib.entity.util.IVariantTypes.writeType(IVariantTypes.java:41) ~[?:9.0.1] {re:classloading}
at its_meow.betteranimalsplus.common.entity.util.abstracts.EntityAnimalWithTypes.func_184198_c(EntityAnimalWithTypes.java:30) ~[?:9.0.1] {re:classloading}
at net.minecraft.entity.Entity.func_70039_c(Entity.java:1332) ~[?:?] {re:classloading,pl:accesstransformer:B}
at net.minecraft.world.chunk.ChunkPrimer.func_76612_a(ChunkPrimer.java:216) ~[?:?] {re:classloading}
at net.minecraft.world.gen.WorldGenRegion.func_217376_c(WorldGenRegion.java:252) ~[?:?] {re:classloading}
at net.minecraft.world.spawner.WorldEntitySpawner.func_77191_a(WorldEntitySpawner.java:370) ~[?:?] {re:classloading}
at net.minecraft.world.gen.NoiseChunkGenerator.func_230354_a_(NoiseChunkGenerator.java:614) ~[?:?] {re:classloading}
at net.minecraft.world.chunk.ChunkStatus.lambda$static$12(ChunkStatus.java:89) ~[?:?] {re:classloading,pl:accesstransformer:B}
at net.minecraft.world.chunk.ChunkStatus$$Lambda$2196/990826507.doWork(Unknown Source) ~[?:?] {}
at net.minecraft.world.chunk.ChunkStatus$ISelectiveWorker.doWork(ChunkStatus.java:240) ~[?:?] {re:classloading}
at net.minecraft.world.chunk.ChunkStatus.func_223198_a(ChunkStatus.java:198) ~[?:?] {re:classloading,pl:accesstransformer:B}
at net.minecraft.world.server.ChunkManager.lambda$null$18(ChunkManager.java:691) ~[?:?] {re:classloading,xf:OptiFine:default}
at net.minecraft.world.server.ChunkManager$$Lambda$5175/216863107.apply(Unknown Source) ~[?:?] {}
at com.mojang.datafixers.util.Either$Left.map(Either.java:38) ~[datafixerupper-3.0.25.jar:?] {}
at net.minecraft.world.server.ChunkManager.lambda$chunkGenerate$20(ChunkManager.java:689) ~[?:?] {re:classloading,xf:OptiFine:default}
at net.minecraft.world.server.ChunkManager$$Lambda$5160/334857863.apply(Unknown Source) ~[?:?] {}
at java.util.concurrent.CompletableFuture.uniCompose(CompletableFuture.java:952) ~[?:1.8.0_51] {}
at java.util.concurrent.CompletableFuture$UniCompose.tryFire(CompletableFuture.java:926) ~[?:1.8.0_51] {}
at java.util.concurrent.CompletableFuture$Completion.run(CompletableFuture.java:442) ~[?:1.8.0_51] {}
at net.minecraft.world.chunk.ChunkTaskPriorityQueueSorter.func_219083_b(SourceFile:58) ~[?:?] {re:classloading}
at net.minecraft.world.chunk.ChunkTaskPriorityQueueSorter$$Lambda$5173/1251119799.run(Unknown Source) ~[?:?] {}
at net.minecraft.util.concurrent.DelegatedTaskExecutor.func_213148_e(SourceFile:94) ~[?:?] {re:classloading}
at net.minecraft.util.concurrent.DelegatedTaskExecutor.func_213145_a(SourceFile:137) ~[?:?] {re:classloading}
at net.minecraft.util.concurrent.DelegatedTaskExecutor.run(SourceFile:105) ~[?:?] {re:classloading}
at java.util.concurrent.ForkJoinTask$RunnableExecuteAction.exec(ForkJoinTask.java:1402) ~[?:1.8.0_51] {}
at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289) ~[?:1.8.0_51] {}
at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1056) ~[?:1.8.0_51] {}
at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1689) ~[?:1.8.0_51] {}
at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:157) ~[?:1.8.0_51] {}

A detailed walkthrough of the error, its code path and all known details is as follows:

-- Head --
Thread: Server thread
Stacktrace:
at net.minecraft.nbt.StringNBT.func_229705_a_(StringNBT.java:40)
at net.minecraft.nbt.CompoundNBT.func_74778_a(CompoundNBT.java:150)
at dev.itsmeow.betteranimalsplus.imdlib.entity.util.IVariantTypes.writeType(IVariantTypes.java:41)
at its_meow.betteranimalsplus.common.entity.util.abstracts.EntityAnimalWithTypes.func_184198_c(EntityAnimalWithTypes.java:30)
at net.minecraft.entity.Entity.func_70039_c(Entity.java:1332)
at net.minecraft.world.chunk.ChunkPrimer.func_76612_a(ChunkPrimer.java:216)
at net.minecraft.world.gen.WorldGenRegion.func_217376_c(WorldGenRegion.java:252)
at net.minecraft.world.spawner.WorldEntitySpawner.func_77191_a(WorldEntitySpawner.java:370)
at net.minecraft.world.gen.NoiseChunkGenerator.func_230354_a_(NoiseChunkGenerator.java:614)
at net.minecraft.world.chunk.ChunkStatus.lambda$static$12(ChunkStatus.java:89)
at net.minecraft.world.chunk.ChunkStatus$$Lambda$2196/990826507.doWork(Unknown Source)
at net.minecraft.world.chunk.ChunkStatus$ISelectiveWorker.doWork(ChunkStatus.java:240)
at net.minecraft.world.chunk.ChunkStatus.func_223198_a(ChunkStatus.java:198)

-- Chunk to be generated --
Details:
Location: 67,-56
Position hash: -240518168509
Generator: net.minecraft.world.gen.NoiseChunkGenerator@7ba05d94
Stacktrace:
at net.minecraft.world.server.ChunkManager.lambda$null$18(ChunkManager.java:691)
at net.minecraft.world.server.ChunkManager$$Lambda$5175/216863107.apply(Unknown Source)
at com.mojang.datafixers.util.Either$Left.map(Either.java:38)
at net.minecraft.world.server.ChunkManager.lambda$chunkGenerate$20(ChunkManager.java:689)
at net.minecraft.world.server.ChunkManager$$Lambda$5160/334857863.apply(Unknown Source)
at java.util.concurrent.CompletableFuture.uniCompose(CompletableFuture.java:952)
at java.util.concurrent.CompletableFuture$UniCompose.tryFire(CompletableFuture.java:926)
at java.util.concurrent.CompletableFuture$Completion.run(CompletableFuture.java:442)
at net.minecraft.world.chunk.ChunkTaskPriorityQueueSorter.func_219083_b(SourceFile:58)
at net.minecraft.world.chunk.ChunkTaskPriorityQueueSorter$$Lambda$5173/1251119799.run(Unknown Source)
at net.minecraft.util.concurrent.DelegatedTaskExecutor.func_213148_e(SourceFile:94)

-- Affected level --
Details:
All players: 1 total; [ServerPlayerEntity['FUZEmc'/244, l='ServerLevel[Test]', x=872.86, y=80.30, z=-682.74]]
Chunk stats: ServerChunkCache: 4773
Level dimension: minecraft:overworld
Level spawn location: World: (-1,63,-16), Chunk: (at 15,3,0 in -1,-1; contains blocks -16,0,-16 to -1,255,-1), Region: (-1,-1; contains chunks -32,-32 to -1,-1, blocks -512,0,-512 to -1,255,-1)
Level time: 2488 game time, 2488 day time
Level name: Test
Level game mode: Game mode: creative (ID 1). Hardcore: false. Cheats: true
Level weather: Rain time: 20986 (now: false), thunder time: 13435 (now: false)
Known server brands: forge
Level was modded: true
Level storage version: 0x04ABD - Anvil
Stacktrace:
at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:858)
at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:791)
at net.minecraft.server.integrated.IntegratedServer.func_71217_p(IntegratedServer.java:121)
at net.minecraft.server.MinecraftServer.func_240802_v_(MinecraftServer.java:643)
at net.minecraft.server.MinecraftServer.lambda$func_240784_a_$0(MinecraftServer.java:230)
at net.minecraft.server.MinecraftServer$$Lambda$4982/1561386756.run(Unknown Source)
at java.lang.Thread.run(Thread.java:745)

-- System Details --
Details:
Minecraft Version: 1.16.1
Minecraft Version ID: 1.16.1
Operating System: Windows 10 (amd64) version 10.0
Java Version: 1.8.0_51, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 4360204816 bytes (4158 MB) / 8589934592 bytes (8192 MB) up to 8589934592 bytes (8192 MB)
CPUs: 8
JVM Flags: 9 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xss1M -Xmx8G -XX:+UnlockExperimentalVMOptions -XX:+UseG1GC -XX:G1NewSizePercent=20 -XX:G1ReservePercent=20 -XX:MaxGCPauseMillis=50 -XX:G1HeapRegionSize=32M
ModLauncher: 5.1.0+69+master.79f13f7
ModLauncher launch target: fmlclient
ModLauncher naming: srg
ModLauncher services:
/eventbus-2.2.0-service.jar eventbus PLUGINSERVICE
/forge-1.16.1-32.0.66.jar object_holder_definalize PLUGINSERVICE
/forge-1.16.1-32.0.66.jar runtime_enum_extender PLUGINSERVICE
/accesstransformers-2.1.3-shadowed.jar accesstransformer PLUGINSERVICE
/forge-1.16.1-32.0.66.jar capability_inject_definalize PLUGINSERVICE
/forge-1.16.1-32.0.66.jar runtimedistcleaner PLUGINSERVICE
/preview_OptiFine_1.16.1_HD_U_G2_pre4.jar OptiFine TRANSFORMATIONSERVICE
/forge-1.16.1-32.0.66.jar fml TRANSFORMATIONSERVICE
FML: 32.0
Forge: net.minecraftforge:32.0.66
FML Language Providers:
[email protected]
minecraft@1
Mod List:
forge-1.16.1-32.0.66-client.jar Minecraft {[email protected] DONE}
betteranimalsplus-1.16.1-9.0.1.3.jar Better Animals Plus {[email protected] DONE}
forge-1.16.1-32.0.66-universal.jar Forge {[email protected] DONE}
Player Count: 1 / 8; [ServerPlayerEntity['FUZEmc'/244, l='ServerLevel[Test]', x=872.86, y=80.30, z=-682.74]]
Data Packs: vanilla, mod:betteranimalsplus (incompatible), mod:forge (incompatible)
Type: Integrated Server (map_client.txt)
Is Modded: Definitely; Client brand changed to 'forge'
OptiFine Version: OptiFine_1.16.1_HD_U_G2_pre4
OptiFine Build: 20200711-211327
Render Distance Chunks: 16
Mipmaps: 4
Anisotropic Filtering: 1
Antialiasing: 0
Multitexture: false
Shaders: projectLUMA.zip
OpenGlVersion: 4.6.0 NVIDIA 451.67
OpenGlRenderer: GeForce GTX 1080 Ti/PCIe/SSE2
OpenGlVendor: NVIDIA Corporation
CpuCount: 8`

Versions:

• Minecraft Version: 1.16.1
• Forge Version: 1.16.1 (32.0.66)
• Mod Version: 1.16.1 Github Build

Additional context
Tried with other mods originally which made me discover the crash. Then tried this mod by itself with no other mods, same crash result. If you need anything to help fix the problem, just let me know. Thanks.

This crash is (probably?) fixed in 276c289, it's not on 1.16 yet however, only our 1.14 alpha builds.

Update on this, I've identified the root cause, it's a combination of factors from what was fixed in 276c289 and a bug in IMDLib that I've just resolved. It's not fixed on 1.16 yet, but since 1.16 is purely in development and not out for public release, I'm closing this issue.