code: public static String getContextProperty(Root root, String propertyName) {
          String result = "";
          List<Context> contexts = root.getContexts();
          for (Context context : contexts) {
              String key = context.getKey();
              if (key != null && key.equals(propertyName)) {
                  result = (String) context.getValue();
                  break;
              }
          }
          return result;
      }
docs: return the customProperty from the root object of the input data graph
  
  @param root
  @param propertyName
  @return