code: @Override
      public void configFields(Configuration conf, String[] fields) throws IOException {
          if (null != fields) {
              super.configFields(conf, fields);
              for (int i = 0; i < fields.length; i++) {
                  if(fields[i].trim().equals("")) continue;
                  if (!XML11Char.isXML11ValidName(fields[i])) {
                      fields[i] = XMLUtil.getValidName(fields[i]);
                  }
              }
          } else {
              throw new IOException("Fields not defined");
          }
      }
docs: /*
  @see com.marklogic.contentpump.DocBuilder#checkDocumentHeader()
  @throws IOException