Steps to reproduce:

1. Define a simple content app with a product field.
2. Create 2 entries in the app
3. Use the JCR app to simulate one entry with the old structure and one with the new product structure like this:

OLD: commercetools/magnolia-services-media-demo/bd43e83b-f0ca-46fd-9ebc-f5deae14b646

NEW: {"definitionName":"commercetools","connectionName":"magnolia-services-media-demo","categoryId":"4d7a73d2-f3bd-475b-9dbe-74888a265d69","productId":"87a4d184-3635-4edc-8ba5-022e7b197b5a"}

       4. Try to open both entries

Expected result:

It should be possible to open both nodes. If there is an old structure in JCR, I need to have the chance as an author to change the old data in the new structure.

Actual result:

The App is breaking completely with the attached error and the author is not able to change the old data or use this node at all.