JuniorTheoryCommon

What does tsc report for this program?

TypeScript

let title: string = "Report";
title = null;
console.log(title);

An error: null cannot be assigned to the string type

Expecting null to fit any type, as in JavaScript or with strict mode off: under strict, null has its own type, and string does not accept it.
Blaming the let: a let may take a new value of its declared type; here only null breaks the string declaration.

How do you declare a variable that may hold either a string or null?
Which compiler option makes null and undefined separate types, and which flag turns it on?

JuniorTheoryCommon

TypeScript

let title: string = "Report";
title = null;
console.log(title);

An error: null cannot be assigned to the string type

Expecting null to fit any type, as in JavaScript or with strict mode off: under strict, null has its own type, and string does not accept it.
Blaming the let: a let may take a new value of its declared type; here only null breaks the string declaration.

How do you declare a variable that may hold either a string or null?
Which compiler option makes null and undefined separate types, and which flag turns it on?