Flowable Modeler: export/import of CMMN diagram loses edges

I have a very basic CMMN diagram, with one Task connected to one Milestone.

Exporting the diagram from the Modeler, and importing it again results in the edge losing its source.

Message in the console:
`o.f.c.e.j.c.CmmnJsonConverter : Skipping edge CMMNEdge_sid-9BDC8203-B907-435D-9C12-F16962A0AB63 because source ref is null`

I attach the exported diagram:

[Test_Case.cmmn.xml.zip](https://github.com/flowable/flowable-engine/files/3425718/Test_Case.cmmn.xml.zip)