code: public DynamicReportBuilder addChart(ar.com.fdvs.dj.domain.chart.DJChart djChart) {
          report.getNewCharts().add(djChart);
          return this;
      }
docs: Registers a field that is not necesary bound to a column, it can be used
  in a custom expression
  
  @param djChart a DJ chart
  @return A Dynamic Report Builder