docs: def _to_dict(self):
          """Return a json dictionary representing this model."""
          _dict = {}
          if hasattr(self, 'cell_id') and self.cell_id is not None:
              _dict['cell_id'] = self.cell_id
          if hasattr(self, 'location') and self.location is not None:
              _dict['location'] = self.location
          if hasattr(self, 'text') and self.text is not None:
              _dict['text'] = self.text
          if hasattr(self,
                     'row_index_begin') and self.row_index_begin is not None:
              _dict['row_index_begin'] = self.row_index_begin
          if hasattr(self, 'row_index_end') and self.row_index_end is not None:
              _dict['row_index_end'] = self.row_index_end
          if hasattr(
                  self,
                  'column_index_begin') and self.column_index_begin is not None:
              _dict['column_index_begin'] = self.column_index_begin
          if hasattr(self,
                     'column_index_end') and self.column_index_end is not None:
              _dict['column_index_end'] = self.column_index_end
          return _dict