code: @Nonnull
    public static ServletAsyncSpec createAsync (@CheckForSigned final long nTimeoutMillis,
                                                @Nullable final Iterable <? extends AsyncListener> aAsyncListeners)
    {
      return new ServletAsyncSpec (true, nTimeoutMillis, aAsyncListeners);
    }
docs: Create an async spec.
  
  @param nTimeoutMillis
  Timeout in milliseconds. Only value &gt; 0 are considered.
  @param aAsyncListeners
  The async listeners to use. May be <code>null</code>.
  @return A new {@link ServletAsyncSpec} and never <code>null</code>.