It looks like since 3.7 there is no classes folder in webapp/WEB-INF. This makes the startup fail if using an extension that calls a method from RefineServlet. I probably missed when this change was made. Is there a way for an extension to use RefineServlet now or has that been removed?
This seems to have been a problem with the zip archive uploaded to the extension release. I've uploaded a new version and I'm not seeing an error. This can be closed.