Returns the operator that best matches the type and value.
        
        :param      operatorType | <Query.Op>
                    value        | <variant>
        
        :return     <str>

def operator(self, operatorType, value):
        """
        Returns the operator that best matches the type and value.
        
        :param      operatorType | <Query.Op>
                    value        | <variant>
        
        :return     <str>
        """
        if value is None:
            if 'is none' in self._operatorMap and operatorType == Query.Op.Is:
                return 'is none'
            elif 'is not none' in self._operatorMap:
                return 'is not none'
            
        for op, data in self._operatorMap.items():
            if data.op == operatorType:
                return op
        return ''