To be honest, this is more of a question about how best to handle errors in asynchronous event handlers (not handlers marked as async, I mean like send an email

To be honest, this is more of a question about how best to handle errors in asynchronous event handlers (not handlers marked as async, I mean like send an email at xyz time). Imo best way to solve this is to get notified of an error in sentry, be it an NPE or validation error. In a case where the client expects an immediate response (http GET) getting “400 validation error: foo is not allowed to be null” is a lot more meaningful than “500 Null pointer”. In general I try not to model invalid states - less mental overhead (no one has to tell you xyz can’t be null it just cannot be null). Ofc this is a matter of opinion and the lines get blurred as soon ad you move stuff to runtime.