code: public JsonObject merge(JsonObject object) {
      if (object == null) {
        throw new NullPointerException(OBJECT_IS_NULL);
      }
      for (Member member : object) {
        this.set(member.name, member.value);
      }
      return this;
    }
docs: Copies all members of the specified object into this object. When the specified object contains
  members with names that also exist in this object, the existing values in this object will be
  replaced by the corresponding values in the specified object.
  
  @param object
  the object to merge
  @return the object itself, to enable method chaining