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

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)

Start in the demo's PullToRefreshActivity.java at line 262 and inspect the delayed runnable shown in the stack trace. Run the “Debug Pull to refresh” demo to reproduce the NullPointerException, then verify that the demo no longer crashes when that runnable executes.

Written by the indexing model from the issue text.