NullPointerException: Attempt to invoke virtual method 'int java.lang.String.hashCode()' on a null object reference

[sarankumar-ns]

Caused by java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.String.hashCode()' on a null object reference
       at com.krishna.fileloader.request.FileLoadRequest.hashCode(FileLoadRequest.java:2)
       at java.util.WeakHashMap.hash(WeakHashMap.java:298)
       at java.util.WeakHashMap.getEntry(WeakHashMap.java:426)
       at java.util.WeakHashMap.containsKey(WeakHashMap.java:417)
       at com.krishna.fileloader.FileLoader.addRequestListenerToQueue(FileLoader.java:4)
       at com.krishna.fileloader.request.FileLoadRequest.getRequestListener(FileLoadRequest.java)
       at com.krishna.fileloader.builder.FileLoaderBuilder.asFile(FileLoaderBuilder.java:12)
       at tamilnadu.school.textbook.BookViewerActivity.onCreate(BookViewerActivity.java:12)
       at android.app.Activity.performCreate(Activity.java:7147)
       at android.app.Activity.performCreate(Activity.java:7138)
       at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1219)
       at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2885)
       at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3010)
       at android.app.ActivityThread.-wrap11(ActivityThread.java)
       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1707)
       at android.os.Handler.dispatchMessage(Handler.java:106)
       at android.os.Looper.loop(Looper.java:192)
       at android.app.ActivityThread.main(ActivityThread.java:6759)
       at java.lang.reflect.Method.invoke(Method.java)
       at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:556)
       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:875)