code: protected Runnable wrapTask(Runnable command) {
      final Callable<Object> wrapped = wrapTask(
          Executors.callable(command, null));
      return new Runnable() {
        @Override public void run() {
          try {
            wrapped.call();
          } catch (Exception e) {
            Throwables.propagate(e);
          }
        }
      };
    }
docs: Wraps a {@code Runnable} for submission to the underlying executor. The
  default implementation delegates to {@link #wrapTask(Callable)}.