Unclear on how to use Vue.set() with base store state.

[chckn33]

I'm working on migrating over an existing Nuxt app from Vuex to Pinia, and have been unable to find a way to initialize a store's base state with the Vue.set() method. I tried setting it through an action:

actions: {
     init(foo) {
          Vue.set(this.$state, foo.name, foo.data)
     }
}

I've also tried setting it in middleware:

const fooStore = useFooStore(context.$pinia)
Vue.set(fooStore, 'foo', {bar: 'bar'})

However if I try to set an existing state property, that seems to work.

Vue.set(fooStore.bar, 'foo', {bar: 'bar'})

I know that defining the state would be a better option, but at the moment would cause a lengthy rewrite. Is it possible to use set() with the base state?