ignoreNullForField example

$criteria = [];
        $hasIgnorableNullValue = false;

        foreach ($fields as $fieldName) {
            if (!$class->hasField($fieldName) && !$class->hasAssociation($fieldName)) {
                throw new ConstraintDefinitionException(sprintf('The field "%s" is not mapped by Doctrine, so it cannot be validated for uniqueness.', $fieldName));
            }

            $fieldValue = $class->reflFields[$fieldName]->getValue($entity);

            if (null === $fieldValue && $this->ignoreNullForField($constraint, $fieldName)) {
                $hasIgnorableNullValue = true;

                continue;
            }

            $criteria[$fieldName] = $fieldValue;

            if (null !== $criteria[$fieldName] && $class->hasAssociation($fieldName)) {
                /* Ensure the Proxy is initialized before using reflection to * read its identifiers. This is necessary because the wrapped * getter methods in the Proxy are being bypassed. */