code: private function fillSource($source, $photo): string
      {
          if (! empty($source)) {
              return $this->filterUriInstance($source);
          }
  
          return (string) $photo;
      }
docs: source taken from photo url if not available
  
  @param \Psr\Http\Message\UriInterface|string $source
  @param \Psr\Http\Message\UriInterface|string $photo