[C.7.0] Cannot display BPMNEdge without bpmnElement attribute

[barmac]

In bpmn.io / Camunda Modeler, we don't handle the exception from the rule correctly:

BPMNPlane, BPMNShape, and BPMNEdge MUST reference exactly one abstract syntax BPMN element from the BPMN model using the bpmnElement attribute. The only exception is for a Data Association connected to a Sequence Flow (See Figure 10.68). This is a visual short cut that actually normalizes two Data Associations within the BPMN model. In this case, the resolution is made from the BPMN DI attributes rather than the abstract syntax reference [bpmnElement] (See Table 12.35).
(https://www.omg.org/spec/BPMN/2.0.2/PDF#page=398)

How it should look like:

How it looks:

[barmac]

I cannot add labels to the issue which should be:

• Tool: bpmn.io (Camunda Modeler)
• Test: C.7.0
  The latter seems to not exist yet.