Looses multiple result options and transforms only to one

[JanFellner]

class myobject {
	public compare(other: myobject): number | undefined {
		return 0;
	}
}

Current output:

export interface Imyobject {
    compare(other: myobject): number;
}

expected output:

export interface Imyobject {
    compare(other: myobject): number | undefined;
}