code: public static Class<? extends Writable> getNamedOutputValueClass(JobConf conf,
                                                    String namedOutput) {
      checkNamedOutput(conf, namedOutput, false);
      return conf.getClass(MO_PREFIX + namedOutput + VALUE, null,
        Writable.class);
    }
docs: Returns the value class for a named output.
  
  @param conf        job conf
  @param namedOutput named output
  @return class of named output value