def convert_missing_indexer(indexer):
    """
    Reverse convert a missing indexer, which is a dict
    return the scalar indexer and a boolean indicating if we converted
    """
    if isinstance(indexer, dict):
        indexer = indexer['key']
        if isinstance(indexer, bool):
            raise KeyError('cannot use a single bool to index into setitem')
        return indexer, True
    return indexer, False
