Possible to narrow type of object literal property with strictNullChecks?

**TypeScript Version:** Current playground (2.6?) **Code** ```ts type Foo = { bar?: number[]; } let f1: Foo = {}; f1.bar = []; f1.bar.push(0); let f2: Foo = { bar: [] }; f2.bar.push(0); ``` **Expected behavior:** Both references to `.bar` compile successfully. **Actual behavior:** Second reference (`f2.bar.push(0)`) fails with "object is possibly undefined" -- the type of `f2.bar` is still treated as `number[] | undefined` even though it obviously can't be undefined. ---- This might not be an actual *bug* as such but whatever magic allows the compiler to narrow the type of `f1.bar` after assigning to it, should also be able to narrow the type when it was assigned in the literal.