strictNullChecks thinks a value may be null if null is assigned to it in its non-null branch #7630

TypeScript Version:

3853bb8 (master after merging #7140 )

Code

class Prop {
    value: any;
}

var x: Prop | null = null;
if (x === null) {
    ;
}
else if (x.value === null) { // Line 9
    x = null;
}

tsc -t es5 --strictNullChecks ./foo.ts

Expected behavior:

Compiles.

Actual behavior:

foo.ts(9,10): error TS2531: Object is possibly 'null' or 'undefined'.

If the x = null; assignment (line 10) is removed, it does compile, and x is correctly inferred to be non-null in the condition and body of the else-if block. But this assignment should not have any effect on the nullability of x in the else-if condition.