@Override
    protected Expression instantiate(Object oldInstance, Encoder out) {
      return new Expression(oldInstance, oldInstance.getClass(), "new", null);
    }
Returns the Map or Reduce plan
Side effect: the BaseWork returned is also placed in the gWorkMap
@param conf
@param name
@return BaseWork based on the name supplied will return null if name is null
@throws RuntimeException if the configuration files are not proper or if plan can not be loaded
ql/src/java/org/apache/hadoop/hive/ql/exec/Utilities.java