code: public static XStream buildXStream() {
          XStream xStream = new XStream();
          xStream.setMode(XStream.ID_REFERENCES);
          xStream.aliasSystemAttribute("xStreamId", "id");
          xStream.aliasSystemAttribute("xStreamRef", "reference");
          xStream.processAnnotations(SolverConfig.class);
          XStream.setupDefaultSecurity(xStream);
          xStream.allowTypesByRegExp(new String[]{"org\\.optaplanner\\.\\w+\\.config\\..*"});
          return xStream;
      }
docs: Builds the {@link XStream} setup which is used to read/write {@link SolverConfig solver configs} and benchmark configs.
  It should never be used to read/write {@link PlanningSolution solutions}.
  Use XStreamSolutionFileIO for that instead.
  @return never null.