code: protected function initializeProductMediaGalleryValue(array $attr)
      {
  
          // load the row/value/store ID
          $rowId = $attr[MemberNames::ROW_ID];
          $valueId = $attr[MemberNames::VALUE_ID];
          $storeId = $attr[MemberNames::STORE_ID];
  
          // query whether the product media gallery value already exists or not
          if ($entity = $this->loadProductMediaGalleryValueByValueIdAndStoreIdAndRowId($valueId, $storeId, $rowId)) {
              return $this->mergeEntity($entity, $attr);
          }
  
          // simply return the attributes
          return $attr;
      }
docs: Initialize the product media gallery value with the passed attributes and returns an instance.
  
  @param array $attr The product media gallery value attributes
  
  @return array The initialized product media gallery value