websocket plugin has been broken since Openfire 4.1.4. This PR implements the missing code and fixes the issue

    @Override
   public ConnectionConfiguration getConfiguration()
   {
       // TODO Here we run into an issue with the ConnectionConfiguration introduced in Openfire 4:
       //      it is not extensible in the sense that unforeseen connection types can be added.
       //      For now, null is returned, as this object is likely to be unused (its lifecycle is
       //      not managed by a ConnectionListener instance).
       return null;
   }