When a `hash_part_table` has no secondary attributes, this line breaks since `rows_to_hash.to_dict(orient='records')` will return `[]` instead of `[{}]`.

[spapa013]

When a hash_part_table has no secondary attributes, this line breaks since rows_to_hash.to_dict(orient='records') will return [] instead of [{}].
hash_part_tables with no secondary attributes can be useful for semantic notations for methods with no parameters, for example:

class AreaMemberShip(djp.Manual):  # table storing a mapping from functional unit keys to brain area
    definition = """
    -> fuse.ScanSet.Unit
    ---
    brain_area
    """


class AreaConfig(djp.Lookup):  # method table logging different ways of mapping unit_keys to brain areas
    class AreaMemberShip(djp.Part):  # load brain area from the above table AreaMemberShip, this table does not need any secondary keys
        definition = """
        -> master
        ---
        """

Originally posted by @ZhuokunDing in #1 (comment)