I got this crash report when I was trying to obtain the Save Block in Debug Mode. Oh, and what does the Save Block do, anyway?

---- Minecraft Crash Report ----
// There are four lights!

Time: 8/15/15 9:46 AM
Description: Ticking entity

java.lang.NullPointerException: Ticking entity
at acj.a(SourceFile:401)
at yp.k(SourceFile:282)
at yq.m(SourceFile:404)
at biz.m(SourceFile:708)
at rd.r_(SourceFile:1436)
at yq.r_(SourceFile:229)
at biz.r_(SourceFile:114)
at agh.a(SourceFile:1414)
at agh.g(SourceFile:1392)
at agh.j(SourceFile:1285)
at ayy.s(SourceFile:1845)
at ayy.au(SourceFile:879)
at ayy.a(SourceFile:328)
at net.minecraft.client.main.Main.main(SourceFile:125)

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

– Head –
Stacktrace:
at acj.a(SourceFile:401)
at yp.k(SourceFile:282)
at yq.m(SourceFile:404)
at biz.m(SourceFile:708)
at rd.r_(SourceFile:1436)
at yq.r_(SourceFile:229)
at biz.r_(SourceFile:114)
at agh.a(SourceFile:1414)
at agh.g(SourceFile:1392)

– Entity being ticked –
Details:
Entity Type: null (biz)
Entity ID: 4
Entity Name: Randomblock1
Entity's Exact location: 145.68, 71.78, 96.13
Entity's Block location: 145.00,71.00,96.00 - World: (145,71,96), Chunk: (at 1,4,0 in 9,6; contains blocks 144,0,96 to 159,255,111), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
Entity's Momentum: 0.01, 0.00, 0.02
Entity's Rider: ~_ERROR~ NullPointerException: null
Entity's Vehicle: ~_ERROR~ NullPointerException: null
Stacktrace:
at agh.j(SourceFile:1285)

– Affected level –
Details:
Level name: MpServer
All players: 1 total; [biz['Randomblock1'/4, l='MpServer', x=145.68, y=71.78, z=96.13]]
Chunk stats: MultiplayerChunkCache: 81, 81
Level seed: 0
Level generator: ID 05 - debug_all_block_states, ver 0. Features enabled: false
Level generator options:
Level spawn location: 1.00,60.00,1.00 - World: (1,60,1), Chunk: (at 1,3,1 in 0,0; contains blocks 0,0,0 to 15,255,15), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
Level time: 38404 game time, 6000 day time
Level dimension: 0
Level storage version: 0x00000 - Unknown?
Level weather: Rain time: 0 (now: false), thunder time: 0 (now: false)
Level game mode: Game mode: creative (ID 1). Hardcore: false. Cheats: false
Forced entities: 5 total; [xc['item.tile.endBricks'/18, l='MpServer', x=149.72, y=61.00, z=83.25], xc['item.tile.grassPath'/20, l='MpServer', x=147.06, y=61.00, z=95.64], biz['Randomblock1'/4, l='MpServer', x=145.68, y=71.78, z=96.13], xc['item.tile.monsterStoneEgg.stone'/13, l='MpServer', x=140.81, y=61.00, z=93.66], xc['item.tile.grassPath'/14, l='MpServer', x=143.28, y=61.00, z=95.44]]
Retry entities: 0 total; []
Server brand: vanilla
Server type: Integrated singleplayer server
Stacktrace:
at bhb.a(SourceFile:314)
at ayy.b(SourceFile:2297)
at ayy.a(SourceFile:337)
at net.minecraft.client.main.Main.main(SourceFile:125)

– System Details –
Details:
Minecraft Version: 15w33c
Operating System: Windows 10 (amd64) version 10.0
Java Version: 1.8.0_25, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 105928584 bytes (101 MB) / 259608576 bytes (247 MB) up to 1060372480 bytes (1011 MB)
JVM Flags: 6 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx1G -XX:+UseConcMarkSweepGC -XX:+CMSIncrementalMode -XX:-UseAdaptiveSizePolicy -Xmn128M
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
Launched Version: 15w33c
LWJGL: 2.9.4
OpenGL: GeForce GT 610/PCIe/SSE2 GL version 4.5.0 NVIDIA 353.62, NVIDIA Corporation
GL Caps: Using GL 1.3 multitexturing.
Using GL 1.3 texture combiners.
Using framebuffer objects because OpenGL 3.0 is supported and separate blending is supported.
Shaders are available because OpenGL 2.1 is supported.
VBOs are available because OpenGL 1.5 is supported.

Using VBOs: Yes
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)
CPU: 2x Intel(R) Pentium(R) D CPU 3.00GHz