I happened to trigger this bug when i clicked on the multiplayer button in the main menu using Version 1.7.9 of Minecraft. However it appears to be an one off thing as I tried it another 5 times and didn't trigger the bug.

---- Minecraft Crash Report ----
// My bad.

Time: 03/05/14 10:55
Description: Ticking screen

java.lang.NullPointerException: Ticking screen
at en.a(SourceFile:279)
at ej.i(SourceFile:156)
at ej.a(SourceFile:162)
at bmc.a(SourceFile:245)
at bik.c(SourceFile:108)
at ban.p(SourceFile:1343)
at ban.ak(SourceFile:774)
at ban.f(SourceFile:728)
at net.minecraft.client.main.Main.main(SourceFile:148)

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

– Head –
Stacktrace:
at en.a(SourceFile:279)
at ej.i(SourceFile:156)
at ej.a(SourceFile:162)
at bmc.a(SourceFile:245)
at bik.c(SourceFile:108)

– Affected screen –
Details:
Screen name: bik
Stacktrace:
at ban.p(SourceFile:1343)
at ban.ak(SourceFile:774)
at ban.f(SourceFile:728)
at net.minecraft.client.main.Main.main(SourceFile:148)

– System Details –
Details:
Minecraft Version: 1.7.9
Operating System: Windows 8 (amd64) version 6.2
Java Version: 1.7.0_51, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 232921112 bytes (222 MB) / 323485696 bytes (308 MB) up to 7635730432 bytes (7282 MB)
JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx8G
AABB Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
Launched Version: 1.7.9
LWJGL: 2.9.1
OpenGL: GeForce GTX 770/PCIe/SSE2 GL version 4.4.0, NVIDIA Corporation
GL Caps: Using GL 1.3 multitexturing.
Using framebuffer objects because OpenGL 3.0 is supported and separate blending is supported.
Anisotropic filtering is supported and maximum anisotropy is 16.
Shaders are available because OpenGL 2.1 is supported.

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: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
Anisotropic Filtering: Off (1)