Macro returning a MacroBlock is not displayed by the BlockAsyncRenderer

@Component
@Singleton
@Named("test123")
public class TestClass extends AbstractMacro<Object>
{
    @Inject
    private ComponentManager componentManager;

    @Inject
    private BlockAsyncRendererExecutor executor;

    public TestClass()
    {
        super("TestClass");
    }

    @Override
    public boolean supportsInlineMode()
    {
        return false;
    }

    @Override
    public List<Block> execute(Object parameters, String content, MacroTransformationContext context)
        throws MacroExecutionException
    {
        AsyncRendererConfiguration configuration = new AsyncRendererConfiguration();

        Block result = null;

        try {
            TestAsyncRenderer asyncRenderer =
                componentManager.getInstance(TestAsyncRenderer.class);
            asyncRenderer.initialize(this, context);
            result = executor.execute(asyncRenderer, configuration);
        } catch (JobException | RenderingException | ComponentLookupException e) {
            throw new RuntimeException(e);
        }
        return result instanceof CompositeBlock ? result.getChildren() : Collections.singletonList(result);
    }

    public List<Block> internalExecute()
    {
        return Collections.singletonList(new MacroBlock("info", Collections.emptyMap(), "Hello there", false));
    }
}

@Component(roles = TestAsyncRenderer.class)
public class TestAsyncRenderer extends AbstractBlockAsyncRenderer
{
    private TestClass testClass;

    private MacroTransformationContext context;

    private Syntax targetSyntax;

    public void initialize(TestClass testClass, MacroTransformationContext context)
    {
        this.context = context;
        this.testClass = testClass;
        this.targetSyntax = context.getTransformationContext().getTargetSyntax();
    }

    @Override
    protected Block execute(boolean async, boolean cached) throws RenderingException
    {
        List<Block> result = testClass.internalExecute();
        return new GroupBlock(result);
    }

    @Override
    public boolean isInline()
    {
        return false;
    }

    @Override
    public Syntax getTargetSyntax()
    {
        return targetSyntax;
    }

    @Override
    public List<String> getId()
    {
        return createId("test", "async", "renderer", RandomUtils.nextInt());
    }

    @Override
    public boolean isAsyncAllowed()
    {
        return true;
    }

    @Override
    public boolean isCacheAllowed()
    {
        return false;
    }
}