Comment 1 for bug 509577

To resolve this bug you can make a check of the address field in the code.
In file collective/dancing/browser/sendnewsletter.py, line 231 (inside the function handle_preview) you can add the checker test as follows:
        address = data['address']
        if not address:
            self.status = 'The address to send the preview is missing.'
            return