code: public void reset()
      {
          m_currentValue = null;
          useCurrentValue(false);
          setDerived(false);
          m_notKnown = false;
          setUnknown(m_lastUnknown);
      }
docs: /* (non-Javadoc)
  @see nz.co.senanque.validationengine.ProxyField#reset()