crash happen when showing the demo of 'Debug Pull to refresh'

[hi2hcs]

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.LinearLayoutManager.scrollToPosition(int)' on a null object reference
at com.marshalchen.ultimaterecyclerview.demo.loadmoredemo.PullToRefreshActivity$5$1.run(PullToRefreshActivity.java:262)
at android.os.Handler.handleCallback(Handler.java:815)
at android.os.Handler.dispatchMessage(Handler.java:104)
at android.os.Looper.loop(Looper.java:207)
at android.app.ActivityThread.main(ActivityThread.java:5975)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:679)