Crash Log:

[22:13:11] [Server thread/ERROR]: Encountered an unexpected exception
java.lang.NullPointerException
	at net.minecraft.world.gen.feature.WorldGenerator.func_175903_a(SourceFile:31) ~[aud.class:?]
	at net.minecraft.world.gen.feature.WorldGenBigTree.func_181631_a(WorldGenBigTree.java:106) ~[atq.class:?]
	at net.minecraft.world.gen.feature.WorldGenBigTree.func_175940_a(WorldGenBigTree.java:147) ~[atq.class:?]
	at net.minecraft.world.gen.feature.WorldGenBigTree.func_175941_b(WorldGenBigTree.java:201) ~[atq.class:?]
	at net.minecraft.world.gen.feature.WorldGenBigTree.func_180709_b(WorldGenBigTree.java:291) ~[atq.class:?]
	at net.minecraft.world.biome.BiomeForest.func_185379_b(BiomeForest.java:108) ~[aip.class:?]
	at net.minecraft.world.biome.BiomeForest.func_180624_a(BiomeForest.java:74) ~[aip.class:?]
	at teamrtg.rtg.api.world.gen.RealisticBiomeGenerator.decorateBaseBiome(RealisticBiomeGenerator.java:168) ~[RealisticBiomeGenerator.class:?]
	at teamrtg.rtg.api.world.biome.deco.DecoBaseBiomeDecorations.generate(DecoBaseBiomeDecorations.java:83) ~[DecoBaseBiomeDecorations.class:?]
	at teamrtg.rtg.api.world.gen.RealisticBiomeGenerator.decorate(RealisticBiomeGenerator.java:309) ~[RealisticBiomeGenerator.class:?]
	at teamrtg.rtg.core.world.ChunkProviderRTG.func_185931_b(ChunkProviderRTG.java:433) ~[ChunkProviderRTG.class:?]
	at net.minecraft.world.chunk.Chunk.func_186034_a(Chunk.java:1005) ~[asf.class:?]
	at net.minecraft.world.chunk.Chunk.func_186030_a(Chunk.java:988) ~[asf.class:?]
	at net.minecraft.world.gen.ChunkProviderServer.func_186025_d(ChunkProviderServer.java:157) ~[lp.class:?]
	at net.minecraft.server.MinecraftServer.func_71222_d(MinecraftServer.java:297) ~[MinecraftServer.class:?]
	at net.minecraft.server.integrated.IntegratedServer.func_71247_a(IntegratedServer.java:105) ~[byl.class:?]
	at net.minecraft.server.integrated.IntegratedServer.func_71197_b(IntegratedServer.java:119) ~[byl.class:?]
	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:429) [MinecraftServer.class:?]
	at java.lang.Thread.run(Unknown Source) [?:1.8.0_92]
[22:13:11] [Server thread/ERROR]: This crash report has been saved to: C:\Users\Simon\Desktop\MultiMC\instances\1.9.41\minecraft\crash-reports\crash-2016-06-16_22.13.11-server.txt
[22:13:11] [Server thread/INFO]: Stopping server
[22:13:11] [Server thread/INFO]: Saving players
[22:13:11] [Server thread/INFO]: Saving worlds
[22:13:11] [Server thread/INFO]: Saving chunks for level 'New World'/Overworld
[22:15:59] [Server thread/INFO]: Saving chunks for level 'New World'/Nether
[22:15:59] [Server thread/INFO]: Saving chunks for level 'New World'/The End
[22:15:59] [Server thread/INFO]: Unloading dimension 0
[22:15:59] [Server thread/INFO]: Unloading dimension -1
[22:15:59] [Server thread/INFO]: Unloading dimension 1
[22:15:59] [Server thread/INFO]: Applying holder lookups
[22:15:59] [Server thread/INFO]: Holder lookups applied
[22:15:59] [Server thread/INFO]: The state engine was in incorrect state SERVER_STARTING and forced into state SERVER_STOPPED. Errors may have been discarded.
[22:16:02] [Client thread/INFO]: [net.minecraft.init.Bootstrap:func_179870_a:557]: ---- Minecraft Crash Report ----
// But it works on my machine.

Time: 6/16/16 10:16 PM
Description: Exception in server tick loop

java.lang.NullPointerException: Exception in server tick loop
	at net.minecraft.world.gen.feature.WorldGenerator.func_175903_a(SourceFile:31)
	at net.minecraft.world.gen.feature.WorldGenBigTree.func_181631_a(WorldGenBigTree.java:106)
	at net.minecraft.world.gen.feature.WorldGenBigTree.func_175940_a(WorldGenBigTree.java:147)
	at net.minecraft.world.gen.feature.WorldGenBigTree.func_175941_b(WorldGenBigTree.java:201)
	at net.minecraft.world.gen.feature.WorldGenBigTree.func_180709_b(WorldGenBigTree.java:291)
	at net.minecraft.world.biome.BiomeForest.func_185379_b(BiomeForest.java:108)
	at net.minecraft.world.biome.BiomeForest.func_180624_a(BiomeForest.java:74)
	at teamrtg.rtg.api.world.gen.RealisticBiomeGenerator.decorateBaseBiome(RealisticBiomeGenerator.java:168)
	at teamrtg.rtg.api.world.biome.deco.DecoBaseBiomeDecorations.generate(DecoBaseBiomeDecorations.java:83)
	at teamrtg.rtg.api.world.gen.RealisticBiomeGenerator.decorate(RealisticBiomeGenerator.java:309)
	at teamrtg.rtg.core.world.ChunkProviderRTG.func_185931_b(ChunkProviderRTG.java:433)
	at net.minecraft.world.chunk.Chunk.func_186034_a(Chunk.java:1005)
	at net.minecraft.world.chunk.Chunk.func_186030_a(Chunk.java:988)
	at net.minecraft.world.gen.ChunkProviderServer.func_186025_d(ChunkProviderServer.java:157)
	at net.minecraft.server.MinecraftServer.func_71222_d(MinecraftServer.java:297)
	at net.minecraft.server.integrated.IntegratedServer.func_71247_a(IntegratedServer.java:105)
	at net.minecraft.server.integrated.IntegratedServer.func_71197_b(IntegratedServer.java:119)
	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:429)
	at java.lang.Thread.run(Unknown Source)


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

-- System Details --
Details:
	Minecraft Version: 1.9.4
	Operating System: Windows 8.1 (amd64) version 6.3
	Java Version: 1.8.0_92, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 1988462760 bytes (1896 MB) / 3102212096 bytes (2958 MB) up to 3817865216 bytes (3641 MB)
	JVM Flags: 3 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xms3072m -Xmx4096m
	IntCache: cache: 0, tcache: 0, allocated: 9, tallocated: 61
	FML: MCP 9.28 Powered by Forge 12.17.0.1964 8 mods loaded, 8 mods active
	States: 'U' = Unloaded 'L' = Loaded 'C' = Constructed 'H' = Pre-initialized 'I' = Initialized 'J' = Post-initialized 'A' = Available 'D' = Disabled 'E' = Errored
	UCHIJAA	mcp{9.19} [Minecraft Coder Pack] (minecraft.jar) 
	UCHIJAA	FML{8.0.99.99} [Forge Mod Loader] (forge-1.9.4-12.17.0.1964-universal.jar) 
	UCHIJAA	Forge{12.17.0.1964} [Minecraft Forge] (forge-1.9.4-12.17.0.1964-universal.jar) 
	UCHIJAA	BiomesOPlenty{4.1.0.2026} [Biomes O' Plenty] (BiomesOPlenty-1.9.4-4.1.0.2026-universal.jar) 
	UCHIJAA	JEI{3.6.3.212} [Just Enough Items] (jei_1.9.4-3.6.3.212.jar) 
	UCHIJAA	harvestcraft{1.9.4-pre} [Pam's HarvestCraft] (Pam's HarvestCraft 1.9.4a.jar) 
	UCHIJAA	RTG{1.9.4-2.0.0-alpha.5} [Realistic Terrain Generation] (RTG-1.9.4-2.0.0-alpha.5.jar) 
	UCHIJAA	Waila{1.7.0} [Waila] (Waila-1.7.0-B3_1.9.4.jar) 
	Loaded coremods (and transformers): 
	GL info: ~~ERROR~~ RuntimeException: No OpenGL context found in the current thread.
	Profiler Position: N/A (disabled)
	Player Count: 0 / 8; []
	Type: Integrated Server (map_client.txt)
	Is Modded: Definitely; Client brand changed to 'fml,forge'
[22:16:02] [Client thread/INFO]: [net.minecraft.init.Bootstrap:func_179870_a:557]: #@!@# Game crashed! Crash report saved to: #@!@# C:\Users\Simon\Desktop\MultiMC\instances\1.9.41\minecraft\crash-reports\crash-2016-06-16_22.13.11-server.txt
[22:16:02] [Client Shutdown Thread/INFO]: Stopping server
AL lib: (EE) alc_cleanup: 1 device not closed