public static function cursorToKey($cursor) {
      if ($decoded = base64_decode($cursor)) {
        return substr($decoded, strlen(self::PREFIX));
      }
      return null;
    }
public static function cursorToKey($cursor) {
      if ($decoded = base64_decode($cursor)) {
        return substr($decoded, strlen(self::PREFIX));
      }
      return null;
    }
public static function cursorToKey ( $ cursor ) { if ( $ decoded = base64_decode ( $ cursor ) ) { return substr ( $ decoded , strlen ( self :: PREFIX ) ) ; } return null ; }
Converts a cursor to its array key.

@param $cursor
@return null|string
Converts a cursor to its array key .