code: public static function normalize(array $files)
      {
          $normalized = array();
  
          foreach ((array) $files as $key => $value) {
              if ($value instanceof UploadedFileInterface) {
                  $normalized[$key] = $value;
              } elseif (isset($value['tmp_name']) === true) {
                  $normalized[$key] = self::create($value);
              } elseif (is_array($value) === true) {
                  $normalized[$key] = self::normalize($value);
              }
          }
  
          return $normalized;
      }
docs: Parses the $_FILES into multiple \UploadedFile instances.
  
  @param  array $files
  @return \Psr\Http\Message\UploadedFileInterface[]