Just happened to me trying to generate a new world (singleplayer).
Crash Report:
---- Minecraft Crash Report ----
// Don't be sad. I'll do better next time, I promise!
Time: 08/05/2023, 19:43
Description: Exception in server tick loop
java.lang.ArrayIndexOutOfBoundsException: Index 6 out of bounds for length 6
at btw.world.feature.trees.grower.BigTreeGrower.generateLeaves(BigTreeGrower.java:324)
at btw.world.feature.trees.grower.BigTreeGrower.growTree(BigTreeGrower.java:30)
at betterterrain.world.generate.surface.SurfaceBuilder.generateTreesForBiome(SurfaceBuilder.java:485)
at betterterrain.world.generate.surface.SurfaceBuilder.generateTrees(SurfaceBuilder.java:154)
at betterterrain.biome.BiomeDecorator.decorate(BiomeDecorator.java:366)
at betterterrain.biome.BiomeDecorator.method_3848(BiomeDecorator.java:274)
at betterterrain.biome.BTABiome.decorate(BTABiome.java:81)
at betterterrain.world.generate.BTADefaultChunkProvider.method_3867(BTADefaultChunkProvider.java:459)
at net.minecraft.class_794.method_3867(class_794.java:237)
at net.minecraft.class_1196.method_3892(class_1196.java:1154)
at net.minecraft.class_794.method_3871(class_794.java:132)
at net.minecraft.server.MinecraftServer.method_3019(MinecraftServer.java:317)
at net.minecraft.class_601.method_2995(class_601.java:91)
at net.minecraft.class_601.method_3011(class_601.java:107)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:458)
at net.minecraft.class_739.run(class_739.java:573)
A detailed walkthrough of the error, its code path and all known details is as follows:
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-- System Details --
Details:
Minecraft Version: 1.5.2
Operating System: Windows 10 (amd64) version 10.0
Java Version: 16.0.2, Oracle Corporation
Java VM Version: OpenJDK 64-Bit Server VM (mixed mode, sharing), Oracle Corporation
Memory: 413109424 bytes (393 MB) / 1073741824 bytes (1024 MB) up to 4294967296 bytes (4096 MB)
JVM Flags: 4 total; -Xverify:none -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xms1024m -Xmx4096m
AABB Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
Suspicious classes: ~~ERROR~~ NoSuchFieldException: classes
IntCache: cache: 0, tcache: 0, allocated: 2, tallocated: 67
Profiler Position: N/A (disabled)
Vec3 Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
Player Count: 0 / 8; []
Type: Integrated Server (map_client.txt)
Is Modded: Definitely; Client brand changed to 'fabric'
Just happened to me trying to generate a new world (singleplayer).
Crash Report:
Generator String: