code: private String parsePhotoId(GraphObject graphObject) {
          String photoId = null;
  
          if (graphObject != null) {
              JSONObject jsonObject = graphObject.getInnerJSONObject();
              if (jsonObject != null) {
                  photoId = jsonObject.optString(SHARE_KEY_PHOTO_ID, null);
              }
          }
          return photoId;
      }
docs: Parses the photo id from a {@link GraphObject}.
  
  @param graphObject the {@link GraphObject} to parse.
  @return the photo id; or null if not found.