docs: def _to_dict(self):
          """Return a json dictionary representing this model."""
          _dict = {}
          if hasattr(self, 'documents') and self.documents is not None:
              _dict['documents'] = self.documents._to_dict()
          if hasattr(self, 'disk_usage') and self.disk_usage is not None:
              _dict['disk_usage'] = self.disk_usage._to_dict()
          if hasattr(self, 'collections') and self.collections is not None:
              _dict['collections'] = self.collections._to_dict()
          return _dict