public TpcEngineBuilder setReactorBuilder(ReactorBuilder reactorBuilder) {
        this.reactorBuilder = checkNotNull(reactorBuilder, "reactorBuilder");
        return this;
    }
@Test
    public void test_setReactorBuilderWhenNull() {
        TpcEngineBuilder builder = new TpcEngineBuilder();
        assertThrows(NullPointerException.class, () -> builder.setReactorBuilder(null));
    }