protected function getEmptyWhereCondition(string $field, array $criteria): array
    {
        $emptyCriteria = $this->searchFields[$field]['operators'][$criteria['operator']]['emptyCriteria'];

        $result = [];
        foreach ($emptyCriteria['values'] as $value) {
            $result[$emptyCriteria['aggregator']][] = $field . ' ' . trim($value);
        }

        return $result;
    }