docs: @Override
      public TemplateModel unmarshal( final String xml ) {
          if ( xml == null || xml.trim().length() == 0 ) {
              return createEmptyModel();
          }
          TemplateModel model = (TemplateModel) this.xt.fromXML( xml );
  
          //Upgrade model changes to legacy artifacts
          ruleModelUpgrader1.upgrade( model );
          ruleModelUpgrader2.upgrade( model );
          ruleModelUpgrader3.upgrade( model );
  
          ruleTemplateModelUpgrader1.upgrade( model );
  
          model.putInSync();
  
          return model;
      }