El-autocomplete concatenate with previous field value instead of replacing it

Hello, I use autocomplete element to provide autocomplete in my vue app, let say I use it for autocomplete Authors
I need to fill multiple author with comma as delimiter
first search query is OK
then, I add ", " to it and search for another author
but when I select the author from dropdown, the field is replaced by new value
what I need for final value is "Ressie Bashirian, Dorris Kling"

How to achieve this?

I've tried using this

```
handleSelect(item) {
console.log(this.model.authors);
if (this.model.authors == null) {
this.model.authors = item.name;
} else {
this.model.authors = `${this.model.authors} ${item.name}`;
}
console.log(this.model.authors);
}
```

and this is my element
```

```
but it doesn't work