DisplayAlert Method causing crash in xamarin.form

I'm using two entry in my xamarin form application. I want to check whenever the user click on a button, if these entries are empty display an error. currently i'm using the following method:

            if (string.IsNullOrEmpty(EnAirflow.Text) || string.IsNullOrEmpty(EnPressure.Text))
        {
            DisplayAlert("Error", "Please fill all required information.", "OK");

        }

The code is working fine in debug mode on emulator. But when I changed it to release mode or create an apk file from it and testing on a physical device it cause crash. Can you please guide me how I can fix the problem.