I ran into this issue as well. It was due to my project using OSGI R6 Annotations, while the AbstractJcrCommerceServiceFactory and the WeRetailCommerceServiceFactory both use the older Felix SCR annotations to populate the Referenced Services.I was able to get around this by using OSGI R6 Annotation...

                Sling Servlets are a great way to expose functionality in a RESTful way.  Using a different framework to expose Service functionality sounds like unnecessary work. http://www.aemcq5tutorials.com/tutorials/sling-servlet-in-aem/

Sling Servlets are a great way to expose functionality in a RESTful way.  Using a different framework to expose Service functionality sounds like unnecessary work. http://www.aemcq5tutorials.com/tutorials/sling-servlet-in-aem/