Possible to narrow type of object literal property with strictNullChecks?

TypeScript Version: Current playground (2.6?)

Code

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.