REST service cannot retrieve details of some products

The REST service for product detail information cannot retrieve the details of some products.

Steps to reproduce:
1. open http://www.demo.test.onehippo.com/rest/browser
2. select REST call URI 'Product detail'
3. select product 'Dental Floss'
4. click 'Execute REST call'

Expected result: I see the JSON reponse about the Dental Floss product
Actual result: nothing happens; under water the REST call returns an Internal Server error

The REST call works fine for the top three products ("Organic Cotton Reusable Lunch Bag", "Birch Wood Compostable Cutlery", and "Recycled Plastic Cups"). For all other products it is broken.