Conversion to number using unary plus doesn't work properly with null

[zaclummys]

TypeScript Version: 2.8.0-dev.20180202

Code

// Test 1
String(null);

// Test 2
Number(null);

// Test 3
'' + null;

// Test 4
+ null;

Expected behavior:
All tests must be ok.

Actual behavior:
Test 4 isn't ok. Typescript says: Object is possibly 'null'.

Playground Link: https://www.typescriptlang.org/play/index.html#src=%2F%2F%20Test%201%0D%0AString(null)%3B%0D%0A%0D%0A%2F%2F%20Test%202%0D%0ANumber(null)%3B%0D%0A%0D%0A%2F%2F%20Test%203%0D%0A''%20%2B%20null%3B%0D%0A%0D%0A%2F%2F%20Test%204%0D%0A%2B%20null%3B

[mhegazy]

#7989 tracks the general operator interaction with nullable types.. but we chose to allow string + null|undefined to enable some debugging scenarios, see #7989 (comment)

[ghost]

Related: #20131 -- although that case is requesting the compiler to be more strict.

[zaclummys]

@mhegazy,
if TypeScript doesn't allow + null, why it's allowed to use Number(null)?

[mhegazy]

I think i miss linked this issue to #7989. we should think about this one more time..

[RyanCavanaugh]

Related #20754

We like the behavior as-is, inconsistency notwithstanding