docs: def get_content_property_by_key(self, content_id, property_key, expand=None, callback=None):
          """
          Returns a content property.
          :param content_id (string): A string containing the id of the property content container.
          :param property_key (string): The key associated with the property requested.
          :param expand (string): OPTIONAL: A comma separated list of properties to expand on the content properties.
                                  Default value: "version"
          :param callback: OPTIONAL: The callback to execute on the resulting data, before the method returns.
                           Default: None (no callback, raw data returned).
          :return: The JSON data returned from the content/{id}/property/{key} endpoint, or the results of the
                   callback. Will raise requests.HTTPError on bad input, potentially.
          """
          params = {}
          if expand:
              params["expand"] = expand
          return self._service_get_request("rest/api/content/{id}/property/{key}".format(id=content_id, key=property_key),
                                           params=params, callback=callback)