Hopper: java.lang.UnsupportedOperationException: JsonNull

java.lang.UnsupportedOperationException: JsonNull
	at com.google.gson.JsonElement.getAsString(JsonElement.java:185)
	at bpw.a(SourceFile:90)
	at bpw.c(SourceFile:113)
	at bpn.b(SourceFile:132)
	at bcf.a(SourceFile:73)
	at azq.a(SourceFile:172)
	at bcf.a(SourceFile:112)
	at azq.d(SourceFile:236)
	at azq.m(SourceFile:211)

---- Minecraft Crash Report ----
// I blame Dinnerbone.

Time: 21.09.13 12:01
Description: Updating screen events

java.lang.UnsupportedOperationException: JsonNull
	at com.google.gson.JsonElement.getAsString(JsonElement.java:185)
	at bpw.a(SourceFile:90)
	at bpw.c(SourceFile:113)
	at bpn.b(SourceFile:132)
	at bcf.a(SourceFile:73)
	at azq.a(SourceFile:172)
	at bcf.a(SourceFile:112)
	at azq.d(SourceFile:236)
	at azq.m(SourceFile:211)
	at awp.o(SourceFile:1256)
	at awp.aa(SourceFile:726)
	at awp.e(SourceFile:677)
	at net.minecraft.client.main.Main.main(SourceFile:104)


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

-- Head --
Stacktrace:
	at com.google.gson.JsonElement.getAsString(JsonElement.java:185)
	at bpw.a(SourceFile:90)
	at bpw.c(SourceFile:113)
	at bpn.b(SourceFile:132)
	at bcf.a(SourceFile:73)
	at azq.a(SourceFile:172)
	at bcf.a(SourceFile:112)
	at azq.d(SourceFile:236)
	at azq.m(SourceFile:211)

-- Affected screen --
Details:
	Screen name: bcf
Stacktrace:
	at awp.o(SourceFile:1256)
	at awp.aa(SourceFile:726)
	at awp.e(SourceFile:677)
	at net.minecraft.client.main.Main.main(SourceFile:104)

-- System Details --
Details:
	Minecraft Version: 13w38c
	Operating System: Windows 7 (amd64) version 6.1
	Java Version: 1.7.0_25, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 41735416 bytes (39 MB) / 343203840 bytes (327 MB) up to 1037959168 bytes (989 MB)
	JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx1G
	AABB Pool Size: 12176 (681856 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
	IntCache: cache: 0, tcache: 0, allocated: 12, tallocated: 94
	Launched Version: 13w38c
	LWJGL: 2.9.0
	OpenGL: AMD M880G with ATI Mobility Radeon HD 4250          GL version 3.2.9712 Compatibility Profile Context, ATI Technologies Inc.
	Is Modded: Probably not. Jar signature remains and client brand is untouched.
	Type: Client (map_client.txt)
	Resource Packs: []
	Current Language: English (US)
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: ~~ERROR~~ NullPointerException: null