Getting a Null Reference Exception when setting the Binding Context to an object.

Hi, I'm new to Xamarin.forms. I'm trying to do the following code.

private async void Submit_Clicked(object sender, EventArgs eventArgs)
{
var registeredUser = (Registration)BindingContext;
await App.Database.AddUserAsync(registeredUser);
await Navigation.PopAsync();
}

Thanks in Advance.