def normalize_values_for_neo4j(dictionary):
    """
    Sanitizes dictionary for neo4j format by making non-existant values be the string 'NULL'

    Parameters
    ----------
    dictionary : dict
        the dictionary to be sanitized

    Returns
    -------
    out : dict
        sanitized dictionary
    """
    out = {}
    for k, v in dictionary.items():
        if isinstance(v, list):
            v = '.'.join(map(str, v))
        if not v:
            v = 'NULL'
        out[k] = v
    return out