code: public PeriodConverter removePeriodConverter(PeriodConverter converter)
              throws SecurityException {
          
          checkAlterPeriodConverters();
          if (converter == null) {
              return null;
          }
          PeriodConverter[] removed = new PeriodConverter[1];
          iPeriodConverters = iPeriodConverters.remove(converter, removed);
          return removed[0];
      }
docs: Removes a converter from the set of converters. If the converter was
  not in the set, no changes are made.
  
  @param converter  the converter to remove, null ignored
  @return replaced converter, or null