code: public String getTemplateFileUrl(String templateId) throws HelloSignException {
          String fileUrl = null;
          String url = BASE_URI + TEMPLATE_FILE_URI + "/" + templateId;
          JSONObject response = httpClient.withAuth(auth).withGetParam(PARAM_GET_URL, "1").get(url).asJson();
          if (response.has("file_url")) {
              try {
                  fileUrl = response.getString("file_url");
              } catch (JSONException ex) {
                  throw new HelloSignException(ex);
              }
          }
          return fileUrl;
      }
docs: Returns a signed URL that can be used to retrieve the file backing a
  template.
  
  @param templateId String Template ID
  @return String URL or null if no file URL can be retrieved
  @throws HelloSignException thrown if there's a problem processing the
  HTTP request or the JSON response.