def clean_strings(lst):
    """Helper function to clean a list of string values for adding to NWB.

    Parameters
    ----------
    lst : list
        A list of (mostly) strings to be prepped for adding to NWB.

    Returns
    -------
    list of str
        Cleaned list.

    Notes
    -----
    Each element is checked:
    - str types and made lower case and kept
    - any other type is replaced with 'none' (as a string)
    - the goal is to replace Python nan or None types for empty cells
    """

    return [val.lower() if isinstance(val, str) else 'none' for val in lst]