Need help resolving a Null Pointer Exception，at com.github.barteksc.pdfviewer.PDFView.loadComplete (PDFView.java:756)

[jonbbs]

Exception java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.os.HandlerThread.isAlive()' on a null object reference
at com.github.barteksc.pdfviewer.PDFView.loadComplete (PDFView.java:756)
at com.github.barteksc.pdfviewer.DecodingAsyncTask.onPostExecute (DecodingAsyncTask.java:80)
at com.github.barteksc.pdfviewer.DecodingAsyncTask.onPostExecute (DecodingAsyncTask.java:27)
at android.os.AsyncTask.finish (AsyncTask.java:771)
at android.os.AsyncTask.-$$Nest$mfinish
at android.os.AsyncTask$InternalHandler.handleMessage (AsyncTask.java:788)
at android.os.Handler.dispatchMessage (Handler.java:106)
at android.os.Looper.loopOnce (Looper.java:226)
at android.os.Looper.loop (Looper.java:313)
at android.app.ActivityThread.main (ActivityThread.java:8772)
at java.lang.reflect.Method.invoke
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run (RuntimeInit.java:571)
at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:1067)