def METHOD_NAME(self, cell: NotebookNode) -> NotebookNode:
    meta = cell.metadata['nbgrader']
    # only add cell type if the checksum has also already been set
    if 'checksum' in meta and 'cell_type' not in meta:
        self.log.warning("Cell does not have a stored cell type! Adding default cell type.")
        meta['cell_type'] = cell.cell_type
    meta['schema_version'] = self.schema_version
    return cell