Having a extra optional type, why its required when its being set as a prop?

Question

so I've recently came across this case, having these 3 interfaces:

interface a {
  id: string,
  name: string
}

interface b {
  id: string,
  name: string,
  age: string,
}

interface c {
  id: string,
  name:string,
  color: string
}

Assinging these types to a variable:

const selectedType: Ref< a | b | c | null> = ref(null);

and having a component (lest call it modal):

<LW2Modal :title="'modal'" v-model:currentType="selectedType" /></LW2Modal>

which its props are:

const props = withDefaults(
    defineProps<{
        currentType: a | b | null
    }>(),
    {},
);

It's giving an error that I'm missing ("c") obviously, but this modal is only intended to modify a | b, I'm doing this TO NOT HAVE MULTIPLE VARIABLES WHEN SELECTING ANY TYPE

is there a way for typescript to accept this?

Thanks guys :)