code: function createParallelIfNeeded(option) {
      if (option.parallel) {
          return;
      }
  
      var hasParallelSeries = false;
  
      zrUtil.each(option.series, function (seriesOpt) {
          if (seriesOpt && seriesOpt.type === 'parallel') {
              hasParallelSeries = true;
          }
      });
  
      if (hasParallelSeries) {
          option.parallel = [{}];
      }
  }
docs: Create a parallel coordinate if not exists.
  @inner