@Override
  public boolean isValid() {
    DebuggerManagerThreadImpl.assertIsManagerThread();
    if (!super.isValid()) {
      return false;
    }
    try {
      if (myStackFrame != null) {
        myStackFrame.location(); //extra check if jdi frame is valid
      }
      return true;
    }
    catch (InvalidStackFrameException e) {
      return false;
    }
  }
@Override
  public boolean isValid()