code: def clean_email_or_username(self):
          
          email_or_username = self.cleaned_data[self.Fields.EMAIL_OR_USERNAME].strip()
  
          if not email_or_username:
              # The field is blank; we just return the existing blank value.
              return email_or_username
  
          email = email_or_username__to__email(email_or_username)
          bulk_entry = len(split_usernames_and_emails(email)) > 1
          if bulk_entry:
              for email in split_usernames_and_emails(email):
                  validate_email_to_link(
                      email,
                      None,
                      ValidationMessages.INVALID_EMAIL_OR_USERNAME,
                      ignore_existing=True
                  )
              email = email_or_username
          else:
              validate_email_to_link(
                  email,
                  email_or_username,
                  ValidationMessages.INVALID_EMAIL_OR_USERNAME,
                  ignore_existing=True
              )
  
          return email
docs: Clean email form field
  
          Returns:
              str: the cleaned value, converted to an email address (or an empty string)