Typed Backbone-style models with `keyof` in Typescript 2.1

keyof.ts

class Model<T> {
	props: T;
	constructor(initial: T | void){
		if (initial) {
			this.props = initial;
		}
	}
	set<K extends keyof T>(propName: K, value: T[K]) {
		this.props[propName] = value;
	}
	get(propName: keyof T) {
		return this.props[propName];
	}
}

class User extends Model<{
	id?: number,
	fullName?: string,
	email?: string
}> {};

const user = new User({
	fullName: 'Victor Widell'
});

user.set('id', 1337);

console.log(user.get('id'), user.get('fullName'));