protected function validateOperatorCondition($operator, $condition, $attribute = null)
    {
        if ($attribute === null) {
            // absence of an attribute indicates that operator has been placed in a wrong position
            $this->addError($this->filterAttributeName, $this->parseErrorMessage('operatorRequireAttribute', ['operator' => $operator]));
            return;
        }

        $internalOperator = $this->filterControls[$operator];

        // check operator type :
        $operatorTypes = $this->operatorTypes[$internalOperator];
        if ($operatorTypes !== '*') {
            $attributeTypes = $this->getSearchAttributeTypes();
            $attributeType = $attributeTypes[$attribute];
            if (!in_array($attributeType, $operatorTypes, true)) {
                $this->addError($this->filterAttributeName, $this->parseErrorMessage('unsupportedOperatorType', ['attribute' => $attribute, 'operator' => $operator]));
                return;
            }
        }

        if (in_array($internalOperator, $this->multiValueOperators, true)) {
            // multi-value operator:
            if (!is_array($condition)) {
                $this->addError($this->filterAttributeName, $this->parseErrorMessage('operatorRequireMultipleOperands', ['operator' => $operator]));
            } else {
                foreach ($condition as $v) {
                    $this->validateAttributeValue($attribute, $v);
                }
            }
        } else {
            // single-value operator :
            $this->validateAttributeValue($attribute, $condition);
        }
    }