Checking !== undefined should suffice for an optional argument

[sophiebits]

This code doesn't type-check:

/* @flow */

function foo(x?: string): string {
    if (x !== undefined) {
        return x;
    }
    return "meow";
}

Changing the conditional to x != null makes the code work, but I believe checking against undefined should suffice because the argument type itself isn't nullable. Also: != undefined doesn't work even though it has the same meaning as != null.

[avikchaudhuri]

Known issue, will fix.

[gabelevi]

@avikchaudhuri fixed this awhile back when he revamped optional types in v0.2.0. Sorry for forgetting to close out the issue!