Put the summary of the bug you're having here
What I expected to happen was...:
Describe what you thought should happen here
What actually happened was...:
Describe what happened here
Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. ...
3. ...
java.lang.NullPointerException: Invalid Biome id
at ags.a(SourceFile:82)
at agq.<init>(SourceFile:26)
at agp.a(SourceFile:52)
at agp.b(SourceFile:61)
at ags.a(SourceFile:61)
at aoo.a(SourceFile:933)
at afs.a(SourceFile:116)
at afs.a(SourceFile:1047)
at bmm.j(SourceFile:1343)
at bmm.a(SourceFile:928)
at bmm.b(SourceFile:816)
at azi.ah(SourceFile:787)
at azi.f(SourceFile:711)
at net.minecraft.client.main.Main.main(SourceFile:152)
Is it only happening on this world or also on other worlds? If it's only this one, please update your save file so that we can investigate possible problems.