code: public ApiApp createApiApp(ApiApp app) throws HelloSignException {
          return new ApiApp(
                  httpClient.withAuth(auth).withPostFields(app.getPostFields()).post(BASE_URI + API_APP_URI).asJson());
      }
docs: Creates a new ApiApp using the properties set on the provided ApiApp.
  
  @param app ApiApp
  @return ApiApp newly created ApiApp
  @throws HelloSignException thrown if there's a problem processing the
  HTTP request or the JSON response.