F# multi-key record sort with null ordering

type Person = { Name: string; Age: int }

let compareNullFirst (a: string) (b: string) =
    match isNull a, isNull b with
    | true, true -> 0
    | true, false -> -1
    | false, true -> 1
    | _ -> System.String.CompareOrdinal(a, b)

// List.sortWith is stable, so equal keys keep input order
let sortPeople (people: Person list) =
    people
    |> List.sortWith (fun x y ->
        match compareNullFirst x.Name y.Name with
        | 0 -> compare x.Age y.Age
        | c -> c)

let sorted = sortPeople [ { Name = "ada"; Age = 36 } ]