Type narrowing still doesn't work for non-locals (e.g. global variables or member variables)

Example of code which should work, but results in a type check error:
 

class NumberProvider {
    private static var data as Number?;
    static function get(defaultValue as Number) as Number {
        if (data == null) {
            data = defaultValue;
        }
        return data; // Error: Object of type 'PolyType<Null or $.Toybox.Lang.Number>' does not match return type '$.Toybox.Lang.Number'.
    }
}

Yes, it is clear that NumberProvider.data is Number? in general, but at the time "return data" is executed, the type checker should realize that data is a Number.

If this code is rewritten using an intermediate local variable, the problem disappears, but that's not a desirable workaround imo.

Since the forum won't let me post the code, I'll post it as an image in a comment. Thanks, Garmin forums!