How to get a totally not nullable object

safe-entity.ts

// Unreliable object 😱
type UnsafePerson = {
    name?: string | null,
    age?: number | null,
}

// Nested unreliable object 😱😱😱
type UnsafeParent = UnsafePerson & { child: UnsafePerson };


// 1. Remove undefined with -? operator
// 2. Use the builtin utility NonNullable to remove null from union
type SafeEntity<T extends object> = { [Key in keyof T]-?: T[Key] extends object ? SafeEntity<T[Key]> : NonNullable<T[Key]> }

type SafePerson = SafeEntity<UnsafePerson>; // { name: string; age: number; } 👍

type SafeParent = SafeEntity<UnsafeParent>; // { name: string; age: number; child: { name: string; age: number; } } 👍