reduceElementKeys example

if (null === $value) {
            return;
        }

        if (!\is_array($value) && !$value instanceof \IteratorAggregate) {
            throw new UnexpectedValueException($value, 'array|IteratorAggregate');
        }

        $collectionElements = [];
        $normalizer = $this->getNormalizer($constraint);
        foreach ($value as $element) {
            if ($fields && !$element = $this->reduceElementKeys($fields, $element)) {
                continue;
            }

            $element = $normalizer($element);

            if (\in_array($element, $collectionElements, true)) {
                $this->context->buildViolation($constraint->message)
                    ->setParameter('{{ value }}', $this->formatValue($value))
                    ->setCode(Unique::IS_NOT_UNIQUE)
                    ->addViolation();

                

if (null === $value) {
            return;
        }

        if (!\is_array($value) && !$value instanceof \IteratorAggregate) {
            throw new UnexpectedValueException($value, 'array|IteratorAggregate');
        }

        $collectionElements = [];
        $normalizer = $this->getNormalizer($constraint);
        foreach ($value as $element) {
            if ($fields && !$element = $this->reduceElementKeys($fields, $element)) {
                continue;
            }

            $element = $normalizer($element);

            if (\in_array($element, $collectionElements, true)) {
                $this->context->buildViolation($constraint->message)
                    ->setParameter('{{ value }}', $this->formatValue($value))
                    ->setCode(Unique::IS_NOT_UNIQUE)
                    ->addViolation();