I have a method decorator that allows to execute a decorated method only once.This function works good,but at my third unit test it failes because it gives undefined but should return first execution result.
This is my decorator:

import "reflect-metadata";

const metadataKey = Symbol("initialized");

function once(
    target: any,
    propertyKey: string,
    descriptor: PropertyDescriptor
) {
    const method = descriptor.value;
    descriptor.value = function (...args) {
        const initialized = Reflect.getMetadata(
            metadataKey,
            target,
            propertyKey
        );

        if (initialized) {
            return;
        }

        Reflect.defineMetadata(metadataKey, true, target, propertyKey);

        method.apply(this, args);
    };
}  

I think the problem is in the return from the if statement,it should return something but idk what.I played a little but got no succes,thats why i beg you for help.
These are the unit tests:

describe('once', () => {
    it('should call method once with single argument', () => {
        class Test {
            data: string;
            @once
            setData(newData: string) {
                this.data = newData;
            }
        }
        const test = new Test();
        test.setData('first string');
        test.setData('second string');
        assert.strictEqual(test.data, 'first string')
    });

    it('should call method once with multiple arguments', () => {
        class Test {
            user: {name: string, age: number};
            @once
            setUser(name: string, age: number) {
                this.user = {name, age};
            }
        }
        const test = new Test();
        test.setUser('John',22);
        test.setUser('Bill',34);
        assert.deepStrictEqual(test.user, {name: 'John', age: 22})
    });

    it('should return always return first execution result', () => {
        class Test {
            @once
            sayHello(name: string) {
                return `Hello ${name}!`;
            }
        }
        const test = new Test();
        test.sayHello('John');
        test.sayHello('Mark');
        assert.strictEqual(test.sayHello('new name'), 'Hello John!')
    })
}); 

Thanks in advance!