code: @CheckForNull
      public JSONArray getPlatformPluginUpdates() {
          final VersionNumber version = getCurrentLevel();
          if (version == null) {
              return null;
          }
          return getPlatformPluginsForUpdate(version, Jenkins.getVersion());
      }
docs: Provides the list of platform plugin updates from the last time
  the upgrade was run.
  @return {@code null} if the version range cannot be retrieved.