Constrained nullable generics are not control flow checked #14415

interface Banana {
    color: 'yellow';
}

class Monkey<T extends Banana | undefined> {
    a: T;

    render() {
        if (this.a) {
            this.a.color; // error Property 'color' does not exists on type 'T'
        }
    }
}

interface BigBanana extends Banana {
}

class BigMonkey extends Monkey<BigBanana> {
    render() {
        if (this.a) {
            this.a.color;
        }
    }
}