@staticmethod
def _resolve_param_duplicates(values, param_defn, _in):
    """ Resolve cases where query parameters are provided multiple times.
            The default behavior is to use the first-defined value.
            For example, if the query string is '?a=1,2,3&a=4,5,6' the value of
            `a` would be "1,2,3".
            However, if 'collectionFormat' is 'multi' then the duplicate values
            are concatenated together and `a` would be "1,2,3,4,5,6".
        """
    if param_defn.get('collectionFormat') == 'multi':
        return ','.join(values)
    return values[0]
