Bug in DisplayActionSheet, when user touches outside to cancel

await DisplayActionSheet ("TEST ACTION SHEET", null, null, "Action A", "Action B");

Causes "index beyond bounds" exception when the user touches outside the popup area. Touching outside means cancel. To fix, provide a cancel text:

var userChoice = await DisplayActionSheet ("TEST ACTION SHEET", "Cancel", null, "Action A", "Action B");

But the "Cancel" text doesn't appear in the popup on iOS, which is fine, except I would prefer to test for null rather than userChoice=="Cancel".

(Also, it's not clear where bugs should be reported.)