@staticmethod
def _negate_comparison(comparison_string, comparator):
    """
        Function for adding Negation operator to relevance query
        :param comparison_string: str
        :param comparator: str
        :return: str
        """
    if comparator.lower() != 'matches' and comparison_string:
        comparison_string = 'NOT ({})'.format(comparison_string)
    return comparison_string
