java.lang.RuntimeException: Unable to start activity ComponentInfo{com.entitcs.office_attendance/com.entitcs.office_attendance.sales.Sales_Customer_List}: android.view.WindowManager$BadTokenException: Unable to add window -- token null is not valid; is your activity running?
	at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:4169)
	at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:4325)
	at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:101)
	at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
	at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
	at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2574)
	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:8762)
	at java.lang.reflect.Method.invoke(Native Method)
	at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:604)
	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1067)
Caused by: android.view.WindowManager$BadTokenException: Unable to add window -- token null is not valid; is your activity running?
	at android.view.ViewRootImpl.setView(ViewRootImpl.java:1764)
	at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:567)
	at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:148)
	at android.app.Dialog.show(Dialog.java:521)
	at com.entitcs.office_attendance.model_classes.GPSTracker.z(Unknown Source:68)
	at com.entitcs.office_attendance.sales.Sales_Customer_List.onCreate(Unknown Source:274)
	at android.app.Activity.performCreate(Activity.java:8591)
	at android.app.Activity.performCreate(Activity.java:8570)
	at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1384)
	at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:4150)
	... 12 more