code: public @CheckForNull Future<FormValidation> updateDirectly(final boolean signatureCheck) {
          if (! getDataFile().exists() || isDue()) {
              return Jenkins.getInstance().getUpdateCenter().updateService.submit(new Callable<FormValidation>() {
                  @Override public FormValidation call() throws Exception {
                      return updateDirectlyNow(signatureCheck);
                  }
              });
          } else {
              return null;
          }
      }
docs: Update the data file from the given URL if the file
  does not exist, or is otherwise due for update.
  Accepted formats are JSONP or HTML with {@code postMessage}, not raw JSON.
  @param signatureCheck whether to enforce the signature (may be off only for testing!)
  @return null if no updates are necessary, or the future result
  @since 1.502