NormalizerBase.php

<?php

namespace Drupal\hal\Normalizer;

use Drupal\serialization\Normalizer\NormalizerBase as SerializationNormalizerBase;
use Symfony\Component\Serializer\Normalizer\DenormalizerInterface;

/**
 * Base class for Normalizers.
 */
abstract class NormalizerBase extends SerializationNormalizerBase implements DenormalizerInterface {
    
    /**
     * {@inheritdoc}
     */
    protected $format = [
        'hal_json',
    ];
    
    /**
     * {@inheritdoc}
     */
    protected function checkFormat($format = NULL) {
        if (isset($this->formats)) {
            @trigger_error('::formats is deprecated in Drupal 8.4.0 and will be removed before Drupal 9.0.0. Use ::$format instead. See https://www.drupal.org/node/2868275', E_USER_DEPRECATED);
            $this->format = $this->formats;
        }
        return parent::checkFormat($format);
    }

}