I keep on getting this error message. Below is a part of it.

java.util.concurrent.ExecutionException: java.lang.NullPointerException
	at java.util.concurrent.FutureTask.report(FutureTask.java:122) ~[?:1.8.0_25]
	at java.util.concurrent.FutureTask.get(FutureTask.java:192) ~[?:1.8.0_25]
	at h.a(SourceFile:46) [h.class:?]
	at bcx.av(SourceFile:960) [bcx.class:?]
	at bcx.a(SourceFile:396) [bcx.class:?]
	at net.minecraft.client.main.Main.main(SourceFile:124) [Main.class:?]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_25]
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_25]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_25]
	at java.lang.reflect.Method.invoke(Method.java:483) ~[?:1.8.0_25]
	at net.minecraft.launchwrapper.Launch.launch(Launch.java:131) [launchwrapper-1.7.jar:?]
	at net.minecraft.launchwrapper.Launch.main(Launch.java:27) [launchwrapper-1.7.jar:?]
Caused by: java.lang.NullPointerException
	at bll.a(SourceFile:454) ~[bll.class:?]
	at fs.a(SourceFile:67) ~[fs.class:?]
	at fs.a(SourceFile:14) ~[fs.class:?]
	at fl$1.run(SourceFile:13) ~[fl$1.class:?]
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) ~[?:1.8.0_25]
	at java.util.concurrent.FutureTask.run(FutureTask.java:266) ~[?:1.8.0_25]
	at h.a(SourceFile:45) ~[h.class:?]
	... 9 more
[15:12:03] [Client thread/FATAL]: Error executing task
java.util.concurrent.ExecutionException: java.lang.NullPointerException
	at java.util.concurrent.FutureTask.report(FutureTask.java:122) ~[?:1.8.0_25]
	at java.util.concurrent.FutureTask.get(FutureTask.java:192) ~[?:1.8.0_25]
	at h.a(SourceFile:46) [h.class:?]
	at bcx.av(SourceFile:960) [bcx.class:?]
	at bcx.a(SourceFile:396) [bcx.class:?]
	at net.minecraft.client.main.Main.main(SourceFile:124) [Main.class:?]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_25]
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_25]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_25]
	at java.lang.reflect.Method.invoke(Method.java:483) ~[?:1.8.0_25]
	at net.minecraft.launchwrapper.Launch.launch(Launch.java:131) [launchwrapper-1.7.jar:?]
	at net.minecraft.launchwrapper.Launch.main(Launch.java:27) [launchwrapper-1.7.jar:?]
Caused by: java.lang.NullPointerException
	at bll.a(SourceFile:454) ~[bll.class:?]
	at fs.a(SourceFile:67) ~[fs.class:?]
	at fs.a(SourceFile:14) ~[fs.class:?]
	at fl$1.run(SourceFile:13) ~[fl$1.class:?]
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) ~[?:1.8.0_25]
	at java.util.concurrent.FutureTask.run(FutureTask.java:266) ~[?:1.8.0_25]
	at h.a(SourceFile:45) ~[h.class:?]