I've seen this as well. I've never looked into too deeply, but I know that when Tomcat reloads the webapp in the dev environment it often has trouble with calls like getClass().getClassLoader().getResourceAsStream(stream). It should never appear after a full Tomcat restart.

Feel free to file a bug -- looks like we could easily eliminate this by migrating to DefaultModule.getResourceStream(String path), which retrieves the file directly from source when running in dev mode.