minecraft command block crash 1.9 clients

[23:38:30] [Client thread/FATAL]: Error executing task
java.util.concurrent.ExecutionException: java.lang.NullPointerException
	at java.util.concurrent.FutureTask.report(FutureTask.java:122) ~[?:1.7.0_80]
	at java.util.concurrent.FutureTask.get(FutureTask.java:188) ~[?:1.7.0_80]
	at g.a(SourceFile:46) [1.9.jar:?]
	at bcf.av(SourceFile:954) [1.9.jar:?]
	at bcf.a(SourceFile:392) [1.9.jar:?]
	at net.minecraft.client.main.Main.main(SourceFile:124) [1.9.jar:?]
Caused by: java.lang.NullPointerException
	at fo.a(SourceFile:74) ~[1.9.jar:?]
	at bks.a(SourceFile:462) ~[1.9.jar:?]
	at fo.a(SourceFile:68) ~[1.9.jar:?]
	at fo.a(SourceFile:15) ~[1.9.jar:?]
	at fh$1.run(SourceFile:13) ~[1.9.jar:?]
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471) ~[?:1.7.0_80]
	at java.util.concurrent.FutureTask.run(FutureTask.java:262) ~[?:1.7.0_80]
	at g.a(SourceFile:45) ~[1.9.jar:?]
	... 3 more