code: public void addRequestProperty(String key, String value) {
          if (connected)
              throw new IllegalStateException("Already connected");
          if (key == null)
              throw new NullPointerException ("key is null");
      }
docs: The following three methods addRequestProperty, getRequestProperty,
  and getRequestProperties were copied from the superclass implementation
  before it was changed by CR:6230836, to maintain backward compatibility.