Convert optional fields of a Typescript interface to nullable

NullableFields.ts

type NullableFields<T> = Required<{
  [K in keyof T]: {} extends Pick<T, K> ? Exclude<T[K], undefined> | null : T[K]
}>

interface Person {
  name: string
  age?: number
}

const person: NullableFields<Person> = {
  name: 'John',
  age: null,
}