Quarkus Extension execute method on startup

Question

I'm using Quarkus 2.13 and I made a simple Quarkus Extension which defines a List<String> through application.properties. I've added this extension into an application and now I need to check if this List is null or empty everytime the application starts.

Is there something similar to

void onStart(@Observes StartupEvent event) {}

to be used for extensions?

I've already read this piece of documentation (https://quarkus.io/version/2.13/guides/writing-extensions#startup-and-shutdown-events) but it didn't help me.

Thanks