def clean_email_or_username(self):
email_or_username = self.cleaned_data[self.Fields.EMAIL_OR_USERNAME].strip()<EOL>if not email_or_username:<EOL><INDENT>return email_or_username<EOL><DEDENT>email = email_or_username__to__email(email_or_username)<EOL>bulk_entry = len(split_usernames_and_emails(email)) > <NUM_LIT:1><EOL>if bulk_entry:<EOL><INDENT>for email in split_usernames_and_emails(email):<EOL><INDENT>validate_email_to_link(<EOL>email,<EOL>None,<EOL>ValidationMessages.INVALID_EMAIL_OR_USERNAME,<EOL>ignore_existing=True<EOL>)<EOL><DEDENT>email = email_or_username<EOL><DEDENT>else:<EOL><INDENT>validate_email_to_link(<EOL>email,<EOL>email_or_username,<EOL>ValidationMessages.INVALID_EMAIL_OR_USERNAME,<EOL>ignore_existing=True<EOL>)<EOL><DEDENT>return email<EOL>
Clean email form field

Returns:
    str: the cleaned value, converted to an email address (or an empty string)