XmlRpcServlet overrides the method "public void init( ServletConfig config ) throws ServletException" of javax.servlet.GenericServlet, but does not call super.init(). This will lead to multiple methods of GenericServlet, which depend on the ServletConfig being set in the config field, returning null, e.g. getServletConfig and getServletContext.
I went through the implementation of GenericServlet and HttpServlet and it seems like those methods are not used, but extendsion of XmlRpcServlet may do, so it makes sense to call super in my opinion.
Added a patch file as proposal for the fix.