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Attempt to read from field 'long org.opencv.core.Mat.nativeObj' on a null object reference
java.lang.NullPointerException: Attempt to read from field 'long org.opencv.core.Mat.nativeObj' on a null object reference	at org.opencv.imgproc.Imgproc.cvtColor(Imgproc.java:1724)	at com.example.pragyan.facefeatures.ExtractFeature.trainSvm(ExtractFeature.java:242)	at com.example.pragyan.facefeatures.ExtractFeature.onOptionsItemSelected(ExtractFeature.java:313)	at android.app.Activity.onMenuItemSelected(Activity.java:2885)	at android.support.v4.app.FragmentActivity.onMenuItemSelected(FragmentActivity.java:403)	at android.support.v7.app.AppCompatActivity.onMenuItemSelected(AppCompatActivity.java:189)	at android.support.v7.view.WindowCallbackWrapper.onMenuItemSelected(WindowCallbackWrapper.java:100)	at android.support.v7.app.AppCompatDelegateImplV7.onMenuItemSelected(AppCompatDelegateImplV7.java:663)	at android.support.v7.view.menu.MenuBuilder.dispatchMenuItemSelected(MenuBuilder.java:811)	at android.support.v7.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:152)	at android.support.v7.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:958)	at android.support.v7.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:948)	at android.support.v7.view.menu.MenuPopupHelper.onItemClick(MenuPopupHelper.java:191)	at android.widget.AdapterView.performItemClick(AdapterView.java:305)	at android.widget.AbsListView.performItemClick(AbsListView.java:1146)	at android.widget.AbsListView$PerformClick.run(AbsListView.java:3053)	at android.widget.AbsListView$3.run(AbsListView.java:3860)	at android.os.Handler.handleCallback(Handler.java:739)	at android.os.Handler.dispatchMessage(Handler.java:95)	at android.os.Looper.loop(Looper.java:135)	at android.app.ActivityThread.main(ActivityThread.java:5254)	at java.lang.reflect.Method.invoke(Native Method)	at java.lang.reflect.Method.invoke(Method.java:372)	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)