code: public MapWritable getValueMapWritable(String label) {
          HadoopObject o = getHadoopObject(VALUE, label, ObjectUtil.MAP, "Map");
          if (o == null) {
              return null;
          }
  
          return (MapWritable) o.getObject();
      }
docs: Get value {@link MapWritable} value
  @param label target label
  @return {@link MapWritable} value of the label. If it is not null.