def create_child_folder(self, folder_name):
        """ Creates a new child folder

        :param str folder_name: name of the new folder to create
        :return: newly created folder
        :rtype: ContactFolder or None
        """

        if not folder_name:
            return None

        if self.root:
            url = self.build_url(self._endpoints.get('root_folders'))
        else:
            url = self.build_url(
                self._endpoints.get('child_folders').format(id=self.folder_id))

        response = self.con.post(url,
                                 data={self._cc('displayName'): folder_name})
        if not response:
            return None

        folder = response.json()

        # Everything received from cloud must be passed as self._cloud_data_key
        return self.__class__(parent=self, **{self._cloud_data_key: folder})
Creates a new child folder

        :param str folder_name: name of the new folder to create
        :return: newly created folder
        :rtype: ContactFolder or None