code: def user_exists(self, username):
          
  
          response = self._get(self.rest_url + "/user",
                               params={"username": username})
  
          if not response.ok:
              return None
  
          return True
docs: Determines if the user exists.
  
          Args:
              username: The user name.
  
  
          Returns:
              bool:
                  True if the user exists in the Crowd application.