Typescript doesn't recognize null check in previous array.filter().

[DrowningElysium]

In a situation a different user has written code that puts the email of a client to the id field as this is needed for the way the multiselect is written. The problem I am facing is that in the interface I have made the type of the email field string | null as we do have clients that haven't yet fully given their information yet. In the old situation they didn't respect a possible null value.

Because of that I thought of trying to fix this with a filter.

const contacts =
  thisClient.value?.contacts
    ?.filter(contact => props.form.contactAttendeeIds.includes(contact.id))
    .filter(contact => contact.email !== null)
    // Typescript still doesn't recognize that this can't be null anymore.
    .map(contact => ({...contact, ...{id: contact.email as string}})) ?? [];

Because it doesn't recognize that the value can no longer be null it still throws type errors in our pipeline.
It this something that can be fixed or a problem I need to tackle differently?

[MartinJohns]

Duplicate of #38390.

Just add a type annotation to make your function a type guard, otherwise it's not used to narrow.