code: protected int getSortFieldIndex() {
          SortParam sp = getSort();
          Integer index = fieldNameToIndex.get(sp.getProperty());
          if (index == null) {
              index = 1;
          }
          return index;
      }
docs: Returns an index of the currently selected sort field.
  
  @return field index (beginning with 1) or 1 if not found in mapping