code: public Double getTotalEstimate(PrimaryWorkitemFilter filter, boolean includeChildProjects) {
          filter = (filter != null) ? filter : new PrimaryWorkitemFilter();
  
          return getRollup("Workitems:PrimaryWorkitem", "Estimate", filter,
                           includeChildProjects);
      }
docs: Retrieves the total estimate for all stories and defects in this project
  optionally filtered.
  
  @param filter               Criteria to filter stories and defects on.
  @param includeChildProjects If true, include open sub projects, otherwise
  only include this project.
  @return total estimate of selected Workitems.