Get City Label

Nested data often has missing pieces. A user may have no address, or an address with no city. Optional chaining lets you read user.address?.city without crashing. Use a clear default when the path is missing.

Treat only null and undefined as missing. An empty string is a real string, but you may choose to map it to a default for display.

Your Task

Return a display label for a user's city.

• Define interface Address { city?: string | null } and interface Person { name: string; address?: Address | null }.
• Write function getCityLabel(p: Person): string.
• If city exists and is not an empty string, return it.
• Otherwise return 'Unknown'.
• Do not mutate the input.