Unable to close out of an asset on Algorand

[nullun]

After adding an asset on an Algorand account and then opting in to that asset, if the account doesn't hold a balance of that asset then they are unable to proceed with the close-out asset transfer transaction. If the account does have a balance for that asset they can untick the "Leave an account maintenance fee" checkbox and it'll perform an asset transfer with the relevent close-out field, resulting in the asset being opted out. An asset transfer transaction should be able to be submitted regardless of the value in the amount field.