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?

Comienza con la reproducción vinculada de TypeScript Playground usando TypeScript 3.7-beta y compara las tres expresiones de narrowing. Investiga el análisis de flujo de control para literales de cadena no vacíos en el comprobador de tipos; se considera terminado cuando la tercera expresión estrecha a para excluir null sin producir un error y el comportamiento está cubierto por una prueba de regresión.