public static function json_base64_decode($st): ?array
  {
    $res = \is_string($st) ? json_decode($st, true) : $st;
    if ( \is_array($res) ){
      foreach ( $res as $i => $a ){
        if ( \is_array($a) ){
          $res[$i] = self::json_base64_decode($a);
        }
        else if ( \is_string($a) ){
          $res[$i] = base64_decode($a);
        }
        else{
          $res[$i] = $a;
        }
      }
      return $res;
    }
    return null;
  }