[bug] PydanticSerializationError on `mcf_str`

[jm-rivera]

bblocks-datacommons-tools/src/bblocks/datacommons_tools/custom_data/models/common.py

Line 49 in db78e09

def mcf_str(value: str | list[str] | None) -> str | None:

def mcf_str(value: str | list[str] | None) -> str | None:
    """Serialise a string or list of strings without adding quotes.

    Args:
        value: A string, list of strings, or None to serialise.

    Returns:
        A comma-delimited string, a single string, or None if input is None or an empty list.
    """
    if value is None:
        return None

    if isinstance(value, list):
        if not value:
            return None  # <-- add something like this to deal with empty lists
        if len(value) == 1:
            return str(value[0])
        return ", ".join(str(item) for item in value)

    return value