Exception when placing a command block

The bug

An exception is logged when placing a command block. The game does not crash.

Error executing task
java.util.concurrent.ExecutionException: java.lang.NullPointerException
	at java.util.concurrent.FutureTask.report(FutureTask.java:122)
	at java.util.concurrent.FutureTask.get(FutureTask.java:192)
	at k.a(SourceFile:200)
	at net.minecraft.server.MinecraftServer.b(SourceFile:706)
	at net.minecraft.server.MinecraftServer.a(SourceFile:661)
	at dga.a(SourceFile:159)
	at net.minecraft.server.MinecraftServer.run(SourceFile:564)
	at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.NullPointerException
	at bjc.w(SourceFile:119)
	at bjg.j(SourceFile:122)
	at bdg.a(SourceFile:172)
	at arh.a(SourceFile:63)
	at arh.a(SourceFile:36)
	at atc.a(SourceFile:186)
	at tf.a(SourceFile:326)
	at ub.a(SourceFile:920)
	at nr.a(SourceFile:53)
	at nr.a(SourceFile:11)
	at ix.a(SourceFile:10)
	at ix$$Lambda$1756/1208270761.run(Unknown Source)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at k.a(SourceFile:199)
	... 5 more