def create_user(self, username, email=None, password=None, **extra_fields):
        if email and self.filter(email=email).count() > 0:
            raise ValueError('User with email "{0}" already exists'.format(email))

        url = settings.BASE_URL + reverse('admin-user-profile',
                                          username=username)
        chat.send(('New user <{url}|{username}> '
                   'with email "{email}" (from create_user)').format(
            url=url,
            username=username,
            email=email))
        return self._create_user(username, email, password,
                                 **extra_fields)