Hey, I had this problem when I start new world on a snapshot but when it completely loads up it does this.
---- Minecraft Crash Report ----
// But it works on my machine.

Time: 11/22/17 8:14 PM
Description: Unexpected error

java.lang.NullPointerException: Unexpected error
at clf$a.playing(SourceFile:510)
at clf.d(SourceFile:235)
at clh.P_(SourceFile:241)
at bmg.m(SourceFile:1250)
at bmg.b(SourceFile:781)
at bmg.a(SourceFile:369)
at net.minecraft.client.main.Main.main(SourceFile:134)

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

– Head –
Thread: Client thread
Stacktrace:
at clf$a.playing(SourceFile:510)
at clf.d(SourceFile:235)
at clh.P_(SourceFile:241)

– Affected level –
Details:
Level name: MpServer
All players: 1 total; [byp['Percevalgraal'/690, l='MpServer', x=-223.50, y=64.00, z=295.50]]
Chunk stats: MultiplayerChunkCache: 497, 497
Level seed: 0
Level generator: ID 00 - default, ver 1. Features enabled: false
Level generator options:
Level spawn location: World: (-221,64,299), Chunk: (at 3,4,11 in -14,18; contains blocks -224,0,288 to -209,255,303), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
Level time: 74 game time, 74 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: 99 total; [ade['Chicken'/68, l='MpServer', x=-297.38, y=74.00, z=306.27], ade['Chicken'/69, l='MpServer', x=-296.50, y=64.00, z=308.50], ade['Chicken'/70, l='MpServer', x=-297.50, y=64.00, z=308.50], ade['Chicken'/71, l='MpServer', x=-298.28, y=74.00, z=306.75], adf['Cow'/101, l='MpServer', x=-289.50, y=67.00, z=215.50], ade['Chicken'/105, l='MpServer', x=-282.50, y=84.00, z=301.50], ade['Chicken'/106, l='MpServer', x=-280.50, y=84.00, z=302.50], ade['Chicken'/107, l='MpServer', x=-280.54, y=83.00, z=298.49], ade['Chicken'/108, l='MpServer', x=-288.46, y=82.92, z=298.51], ado['Sheep'/109, l='MpServer', x=-281.50, y=84.00, z=303.50], ado['Sheep'/110, l='MpServer', x=-283.50, y=84.00, z=304.50], ado['Sheep'/111, l='MpServer', x=-283.50, y=84.00, z=302.50], ado['Sheep'/112, l='MpServer', x=-286.50, y=83.00, z=299.50], ade['Chicken'/113, l='MpServer', x=-289.50, y=63.00, z=319.50], ade['Chicken'/114, l='MpServer', x=-289.50, y=63.00, z=319.50], ade['Chicken'/115, l='MpServer', x=-293.35, y=63.00, z=320.66], ade['Chicken'/116, l='MpServer', x=-290.50, y=63.00, z=315.91], ade['Chicken'/125, l='MpServer', x=-267.50, y=69.00, z=341.50], ade['Chicken'/126, l='MpServer', x=-263.71, y=68.00, z=345.08], ade['Chicken'/127, l='MpServer', x=-260.53, y=71.00, z=342.20], ade['Chicken'/128, l='MpServer', x=-267.50, y=70.00, z=340.50], aft['Peony'/134, l='MpServer', x=-253.13, y=69.00, z=294.23], ade['Chicken'/135, l='MpServer', x=-253.50, y=75.00, z=321.50], ade['Chicken'/136, l='MpServer', x=-254.50, y=76.00, z=321.50], ade['Chicken'/137, l='MpServer', x=-255.50, y=76.00, z=321.50], ade['Chicken'/138, l='MpServer', x=-257.50, y=77.00, z=320.50], ade['Chicken'/158, l='MpServer', x=-236.50, y=73.00, z=329.50], ags['Skeleton'/4254, l='MpServer', x=-290.50, y=20.00, z=242.50], ade['Chicken'/159, l='MpServer', x=-236.50, y=73.00, z=329.50], ade['Chicken'/160, l='MpServer', x=-232.50, y=71.00, z=329.50], ade['Chicken'/161, l='MpServer', x=-232.50, y=72.00, z=330.50], adb['Bat'/4265, l='MpServer', x=-246.78, y=28.41, z=370.11], adb['Bat'/4267, l='MpServer', x=-246.51, y=28.29, z=364.34], ags['Skeleton'/4268, l='MpServer', x=-167.50, y=28.00, z=368.50], ags['Skeleton'/4269, l='MpServer', x=-167.50, y=28.00, z=363.50], ags['Skeleton'/4270, l='MpServer', x=-169.50, y=28.00, z=367.50], ade['Chicken'/189, l='MpServer', x=-218.50, y=75.00, z=262.50], ade['Chicken'/190, l='MpServer', x=-221.50, y=75.00, z=261.50], ade['Chicken'/191, l='MpServer', x=-219.50, y=75.00, z=263.50], ade['Chicken'/192, l='MpServer', x=-222.50, y=75.00, z=261.50], aft['Dandelion'/206, l='MpServer', x=-196.52, y=64.00, z=263.34], aft['Rose Bush'/211, l='MpServer', x=-182.33, y=63.00, z=261.78], aft['Rose Bush'/212, l='MpServer', x=-181.21, y=63.00, z=262.15], adn['Rabbit'/215, l='MpServer', x=-152.50, y=63.00, z=219.50], adn['Rabbit'/216, l='MpServer', x=-155.50, y=63.00, z=216.50], adf['Cow'/227, l='MpServer', x=-143.50, y=67.00, z=351.50], adf['Cow'/228, l='MpServer', x=-147.50, y=68.00, z=353.50], aga['Creeper'/4349, l='MpServer', x=-206.50, y=34.00, z=280.50], adb['Bat'/4371, l='MpServer', x=-298.93, y=23.28, z=285.82], adb['Bat'/4373, l='MpServer', x=-294.55, y=24.99, z=282.49], adb['Bat'/4374, l='MpServer', x=-296.52, y=24.63, z=282.17], adb['Bat'/4380, l='MpServer', x=-157.43, y=16.69, z=295.57], adb['Bat'/4386, l='MpServer', x=-158.12, y=19.03, z=296.19], adb['Bat'/4437, l='MpServer', x=-273.57, y=45.63, z=347.65], ags['Skeleton'/4492, l='MpServer', x=-282.50, y=29.00, z=356.50], ags['Skeleton'/4493, l='MpServer', x=-286.50, y=29.00, z=356.50], ags['Skeleton'/4494, l='MpServer', x=-283.50, y=29.00, z=356.50], ags['Skeleton'/4549, l='MpServer', x=-273.50, y=43.00, z=341.50], ahb['Zombie'/4583, l='MpServer', x=-153.50, y=17.00, z=372.50], aga['Creeper'/4584, l='MpServer', x=-252.50, y=27.00, z=218.50], aga['Creeper'/4585, l='MpServer', x=-256.50, y=27.00, z=221.50], aga['Creeper'/4586, l='MpServer', x=-252.50, y=27.00, z=221.50], aga['Creeper'/4587, l='MpServer', x=-253.50, y=27.00, z=221.50], ags['Skeleton'/4606, l='MpServer', x=-210.50, y=42.00, z=370.50], ahb['Zombie'/4639, l='MpServer', x=-279.95, y=32.00, z=295.50], ags['Skeleton'/4668, l='MpServer', x=-274.50, y=30.00, z=278.50], aga['Creeper'/4669, l='MpServer', x=-279.50, y=30.00, z=280.50], aga['Creeper'/4670, l='MpServer', x=-278.50, y=30.00, z=278.50], ags['Skeleton'/4671, l='MpServer', x=-274.50, y=30.00, z=279.50], ags['Skeleton'/4688, l='MpServer', x=-257.50, y=36.00, z=363.50], aga['Creeper'/4692, l='MpServer', x=-303.50, y=47.00, z=290.50], ahb['Zombie'/4728, l='MpServer', x=-169.50, y=29.00, z=372.50], aga['Creeper'/4759, l='MpServer', x=-207.50, y=47.00, z=357.50], aga['Creeper'/4789, l='MpServer', x=-304.83, y=24.00, z=276.32], ahb['Zombie'/4834, l='MpServer', x=-276.50, y=30.00, z=352.50], ahb['Zombie'/4835, l='MpServer', x=-274.50, y=30.00, z=352.50], ahb['Zombie'/4836, l='MpServer', x=-275.50, y=30.00, z=353.50], aga['Creeper'/4864, l='MpServer', x=-276.50, y=31.00, z=273.50], ahb['Zombie'/4882, l='MpServer', x=-206.50, y=48.00, z=355.50], byp['Percevalgraal'/690, l='MpServer', x=-223.50, y=64.00, z=295.50], aga['Creeper'/4906, l='MpServer', x=-279.50, y=31.00, z=272.50], ags['Skeleton'/4907, l='MpServer', x=-283.50, y=31.00, z=272.50], aga['Creeper'/4951, l='MpServer', x=-259.50, y=38.00, z=256.50], ags['Skeleton'/5009, l='MpServer', x=-261.50, y=23.00, z=230.50], ahb['Zombie'/5010, l='MpServer', x=-262.50, y=23.00, z=229.50], ahb['Zombie'/5015, l='MpServer', x=-292.50, y=26.00, z=277.50], ahb['Zombie'/5022, l='MpServer', x=-302.50, y=52.00, z=318.50], ahb['Zombie'/5023, l='MpServer', x=-301.50, y=52.00, z=318.50], ags['Skeleton'/5024, l='MpServer', x=-300.50, y=52.00, z=319.50], aga['Creeper'/5031, l='MpServer', x=-253.50, y=35.00, z=375.50], agc['Enderman'/5032, l='MpServer', x=-253.50, y=35.00, z=372.50], agz['Witch'/5033, l='MpServer', x=-254.50, y=35.00, z=372.50], agz['Witch'/5034, l='MpServer', x=-256.50, y=35.00, z=372.50], adb['Bat'/1631, l='MpServer', x=-294.30, y=28.13, z=219.89], aga['Creeper'/2370, l='MpServer', x=-235.50, y=34.00, z=348.50], adb['Bat'/2377, l='MpServer', x=-203.69, y=40.58, z=355.82], adb['Bat'/2995, l='MpServer', x=-290.72, y=22.32, z=217.12], ahb['Zombie'/3106, l='MpServer', x=-293.50, y=23.00, z=283.50], adb['Bat'/3860, l='MpServer', x=-258.62, y=26.76, z=222.60]]
Retry entities: 0 total; []
Server brand: vanilla
Server type: Integrated singleplayer server
Stacktrace:
at bwq.a(SourceFile:356)
at bmg.b(SourceFile:1826)
at bmg.a(SourceFile:383)
at net.minecraft.client.main.Main.main(SourceFile:134)

– System Details –
Details:
Minecraft Version: 17w47a
Operating System: Windows 7 (amd64) version 6.1
Java Version: 1.8.0_25, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 229582480 bytes (218 MB) / 553648128 bytes (528 MB) up to 1073741824 bytes (1024 MB)
JVM Flags: 8 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx1G -XX:+UnlockExperimentalVMOptions -XX:+UseG1GC -XX:G1NewSizePercent=20 -XX:G1ReservePercent=20 -XX:MaxGCPauseMillis=50 -XX:G1HeapRegionSize=16M
IntCache: cache: 0, tcache: 0, allocated: 13, tallocated: 95
Launched Version: 17w47a
LWJGL: 3.1.2 build 29
OpenGL: GeForce GT 545/PCIe/SSE2 GL version 4.5.0 NVIDIA 385.69, 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: ~_ERROR~ NullPointerException: null
Profiler Position: N/A (disabled)
CPU: 4x AMD Athlon(tm) II X4 620 Processor