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Attempt to invoke virtual method 'void android.widget.ProgressBar.setVisibility(int)' on a null object reference
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ProgressBar.setVisibility(int)' on a null object reference	at com.example.albertpula.apka3.MainActivity$ReadPic.onPreExecute(MainActivity.java:83)	at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:604)	at android.os.AsyncTask.execute(AsyncTask.java:551)	at com.example.albertpula.apka3.MainActivity.click(MainActivity.java:54)	at com.example.albertpula.apka3.MainActivity_$1.onClick(MainActivity_.java:72)	at android.view.View.performClick(View.java:5198)	at android.view.View$PerformClick.run(View.java:21147)	at android.os.Handler.handleCallback(Handler.java:739)	at android.os.Handler.dispatchMessage(Handler.java:95)	at android.os.Looper.loop(Looper.java:148)	at android.app.ActivityThread.main(ActivityThread.java:5417)	at java.lang.reflect.Method.invoke(Native Method)	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)