code: public ObjectGraph excludeClasses(Class<?>... classes) {
      for (Class<?> c : classes) {
        if (c == null) {
          throw new NullPointerException("Null class not allowed");
        }
        excludedClasses.add(c);
      }
      return this;
    }
docs: Exclude any object that extends from these classes.
  
  @param classes to exclude.
  @return this