Would orElse(Boolean) solve the problem? Something like

    table.sceneProperty().flatMap(Scene::windowProperty).flatMap(Window::showingProperty).orElse(Boolean.FALSE).addListener((v, o, n) -> {
            if (n) updateShowTableColumnHeader();
        });

I didn't actually know of the orElse method until just now, but it feels like a better way to handle potential nulls here... if it works for you.

I will not even pretend to be able to advise you one way or the other. But I can confirm your fix also works. The two tests would then be:

table.sceneProperty().flatMap(Scene::windowProperty).flatMap(Window::showingProperty).orElse(Boolean.FALSE).addListener((v, o, n) -> {
            if (n) updateShowTableColumnHeader();
        });

and (in tryToKeepSearchText()):

comboSettings.sceneProperty().flatMap(Scene::windowProperty).flatMap(Window::showingProperty).orElse(Boolean.FALSE).addListener((v, o, n) -> {
            if (n && defaultName == null)
                handleComboShowing();
        });

Ah good, could you update the PR for that please?

I couldn't see a way to trigger the issue in QuPath without your script, so I think under 'normal' circumstances the null check might not be needed. I think the orElse is less likely to be removed by some future over-enthusiastic attempt at code cleanup.

I couldn't see a way to trigger the issue in QuPath without your script, so I think under 'normal' circumstances the null check might not be needed.

I'm really sorry about all the fuss. Of course it would be one of my scripts that causes such a niche issue ;-)

Ah good, could you update the PR for that please?

Done!

Thanks!