@Override
  protected void validateRequest() {
    if (!params().containsKey("photoreference")) {
      throw new IllegalArgumentException("Request must contain 'photoReference'.");
    }
    if (!params().containsKey("maxheight") && !params().containsKey("maxwidth")) {
      throw new IllegalArgumentException("Request must contain 'maxHeight' or 'maxWidth'.");
    }
  }
A <a href="https://developers.google.com/places/web-service/photos#place_photo_requests">Place
Photo</a> request.
src/main/java/com/google/maps/PhotoRequest.java