try { if (_expr != null) { return _expr.evalRef(env); } else return NullValue.NULL; } catch (RuntimeException e) { rethrow(e, RuntimeException.class); }  return null;
if (_expr != null) return _expr.eval(env); else return NullValue.NULL;
  public Value execute(Env env)  {    try {      if (_expr != null) {        return _expr.evalRef(env);      }      else        return NullValue.NULL;    }    catch (RuntimeException e) {      rethrow(e, RuntimeException.class);    }        return null;  }