BPMN Subprocess size problem in BPMN Example

I have another question and if I need to create a new topic on the forum just tell me. But as I remember in some previous version of GoJS it was possible to prevent that duplicate links are shown or even added to diagram (they were ignored by diagram model I think). Now I can’t find this info anywhere in docs. Can I do that using some GoJS property or I need manually to check if link exist and prevent creating new one?