problem 01

I can't describe exactly but this error has occured once.

When a nether portail reached (netherworld >>> overworld)

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:814)
	at azi.ah(SourceFile:787)
	at azi.f(SourceFile:711)
	at net.minecraft.client.main.Main.main(SourceFile:152)