Waypoints [obj],[obj],... serialized on diagram

[nikku]

Describe the Bug

After creating a new task from an existing one, the resulting diagram contains an illegal waypoints property on a sequenceFlow:

    <sequenceFlow 
      id="SequenceFlow_0hzgt34" 
      sourceRef="Task_01bfdxd" 
      targetRef="Task_00e7wec" 
      waypoints="[object Object],[object Object],[object Object],[object Object]" />

The problem occurs once the resulting connection has a middle segment:

Steps to Reproduce

• Import test diagram
• Model task as show above
• Observe exported XML (example)

Expected Behavior

Properly serialized without waypoints.

Environment

Please complete the following information:

• Browser: Any
• OS: Any
• Library version: v4.0.0-beta.1

[nikku]

Closed via #1085.