def METHOD_NAME(self, cell: NotebookNode) -> NotebookNode:
    if 'nbgrader' not in cell.metadata:
        return cell
    if 'schema_version' not in cell.metadata['nbgrader']:
        cell.metadata['nbgrader']['schema_version'] = 0
    if cell.metadata['nbgrader']['schema_version'] == 0:
        cell = self._upgrade_v0_to_v1(cell)
    if 'nbgrader' not in cell.metadata:
        return cell
    self._remove_extra_keys(cell)
    return cell