Narrowing doesn't recognize string constant as truthy

TypeScript Version: 3.7-beta

Search Terms: cfa narrowing string truthy

Code

declare var a: { b: number } | null

!a || a.b > 3; // works
!a && true || a.b > 3 && true; // works
!a && "a was not defined" || a.b > 3 && "a.b was too big"; // error "Object is possibly null"

Expected behavior:

The narrowings all work

Actual behavior:

The third narrowing does not work and produces an error

Playground Link:
Playground

Related Issues:
I suspect this is a duplicate, as most CFA narrowing bugs are. But I searched as best I could and didn't find any other bugs that matched what was going on here. It seems like typescript doesn't understand that a non-empty string-literal is true in this situation?

Inizia con la riproduzione collegata di TypeScript Playground usando TypeScript 3.7-beta e confronta le tre espressioni di narrowing. Analizza l’analisi del flusso di controllo per i letterali stringa non vuoti nel type checker; il lavoro è completato quando la terza espressione restringe a in modo da escludere null senza generare un errore e il comportamento è coperto da un test di regressione.