code: @FFDCIgnore(IllegalStateException.class)
      private void removeShutdownHook() {
          if (shutdownHook != null) {
              try {
                  Runtime.getRuntime().removeShutdownHook(shutdownHook);
              } catch (IllegalStateException e) {
                  // do nothing.
              }
          }
      }
docs: Remove the shutdown hook previously added by {@link #addShutdownHook}.