Basic Minecraft Code

java.lang.UnsupportedOperationException: Cannot modify readonly attribute
	at om.b(SourceFile:59)
	at ti.a(SourceFile:107)
	at ti.a(SourceFile:290)
	at na.f(SourceFile:1061)
	at aax.a(SourceFile:116)
	at aax.h(SourceFile:234)
	at bht.a(SourceFile:22)
	at bht.a(SourceFile:17)
	at bht.a(SourceFile:12)
	at bhy.a(SourceFile:106)
	at bhy.a(SourceFile:98)
	at bei.a(SourceFile:317)
	at beb.a(SourceFile:834)
	at beb.b(SourceFile:682)
	at atc.R(SourceFile:683)
	at atc.d(SourceFile:616)
	at net.minecraft.client.main.Main.main(SourceFile:82)


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