Crash: Ticking entity - java.lang.IllegalStateException: Unable to get Y-rotated facing of up

[10:58:18] [Server thread/WARN]: Keeping entity minecraft:villager that already exists with UUID 870c581c-f372-4357-acf0-20a876d3c9fd
[10:58:18] [Server thread/WARN]: Keeping entity minecraft:villager that already exists with UUID e6fb96b0-78bc-4daa-b23a-6c3c46df5c10
[10:58:19] [Server thread/ERROR]: Encountered an unexpected exception
f: Ticking entity
	at net.minecraft.server.MinecraftServer.D(SourceFile:638) ~[17w16b.jar:?]
	at net.minecraft.server.MinecraftServer.C(SourceFile:562) ~[17w16b.jar:?]
	at cfz.C(SourceFile:154) ~[17w16b.jar:?]
	at net.minecraft.server.MinecraftServer.run(SourceFile:466) [17w16b.jar:?]
	at java.lang.Thread.run(Thread.java:745) [?:1.8.0_112]
Caused by: java.lang.IllegalStateException: Unable to get Y-rotated facing of up
	at ej.e(SourceFile:136) ~[17w16b.jar:?]
	at apo.a(SourceFile:184) ~[17w16b.jar:?]
	at avs$a.d(SourceFile:428) ~[17w16b.jar:?]
	at asv.a(SourceFile:123) ~[17w16b.jar:?]
	at zk.n(SourceFile:120) ~[17w16b.jar:?]
	at ur.B_(SourceFile:1728) ~[17w16b.jar:?]
	at us.B_(SourceFile:281) ~[17w16b.jar:?]
	at alt.a(SourceFile:1519) ~[17w16b.jar:?]
	at nr.a(SourceFile:720) ~[17w16b.jar:?]
	at alt.h(SourceFile:1497) ~[17w16b.jar:?]
	at alt.k(SourceFile:1380) ~[17w16b.jar:?]
	at nr.k(SourceFile:553) ~[17w16b.jar:?]
	at net.minecraft.server.MinecraftServer.D(SourceFile:634) ~[17w16b.jar:?]
	... 4 more
[10:58:19] [Server thread/ERROR]: This crash report has been saved to: /Users/Admin/Library/Application Support/minecraft/crash-reports/crash-2017-04-22_10.58.19-server.txt
[10:58:19] [Server thread/INFO]: Stopping server
[10:58:19] [Server thread/INFO]: Saving players
[10:58:19] [Server thread/INFO]: Saving worlds
[10:58:19] [Server thread/INFO]: Saving chunks for level 'Tutorial World II'/Overworld
[10:58:20] [Server thread/INFO]: Saving chunks for level 'Tutorial World II'/Nether
[10:58:20] [Server thread/INFO]: Saving chunks for level 'Tutorial World II'/The End