[MSCE c++] mdlElmdscr_fillet 返回 SUCCESS 但是生成的元素是invalid?

选取两条相交直线进行圆弧fillet。虽然mdl函数返回SUCCESS但是却没有生成元素。我使用fillet构建一个EditElementHandle 但却是invalid?

virtual bool    _OnModifyComplete(DgnButtonEventCR ev) override
{

	if (m_hitPoints.size() == 2)
	{

		ElementAgendaR agenda = GetElementAgenda();
		DPoint3d mid_point = DPoint3d::FromWeightedAverage(m_hitPoints.front(), 1, m_hitPoints.back(), 1);

		MSElementP fillet = NULL;
		StatusInt status = mdlElmdscr_fillet(fillet, NULL,
			agenda.GetEntryP(0)->GetElementDescrP(),
			agenda.GetEntryP(1)->GetElementDescrP(),
			roadparams.roadturn_radius,
			&mid_point,
			NULL);
		wprintf(L">>> entered elementmodified function, there are %d number of line elements in the element agenda \n", GetElementAgenda().size());

		wprintf(L">>> is success: %s, the fillet  %s \n", status == SUCCESS ? L"true" : L"false", fillet==NULL? L"is not null":L" is null");
		if (status == SUCCESS)
		{
			EditElementHandle eh(fillet, agenda.GetEntryP(0)->GetDgnModelP());
			if(eh.IsValid())
				eh.AddToModel();
		}
		m_hitPoints.clear();
	}
	return __super::_OnModifyComplete(ev);

}