code: public JSONAPIDocument<List<Pledge>> fetchPageOfPledges(String campaignId, int pageSize, String pageCursor) throws IOException {
      return fetchPageOfPledges(campaignId, pageSize, pageCursor, null);
    }
docs: Retrieve pledges for the specified campaign
  
  @param campaignId id for campaign to retrieve
  @param pageSize   how many pledges to return
  @param pageCursor A cursor retreived from a previous API call, or null for the initial page.
  See {@link #getNextCursorFromDocument(JSONAPIDocument)}
  @return the page of pledges
  @throws IOException Thrown when the GET request failed