vue.js – initial reactive value of origin to null

I have a question about using reactive. I know the type of a state, but the initial value is empty. How do I use assignment? The code is as follows

  let origin = reactive<Timeslot | {}>({});
  const handler = (data) => {
       Object.assign(origin, data);

In fact, I want to assign the initial value of origin to null. How can I deal with this problem?