Allow length to work on optional arrays

Right now:

  input {
    Array[Int] xs = [1, 2, 3]
    Array[Int]? ys = [1, 2, 3]
    Array[Int]? zs # Imagine this doesn't get supplied
  }

  Int len_xs = length(xs) # Returns 3
  Int len_ys = length(ys) # Doesn't work
  Int len_zs = length(zs) # Doesn't work

It seems sensible to me to also allow behavior like:

  input {
    Array[Int] xs = [1, 2, 3]
    Array[Int]? ys = [1, 2, 3]
    Array[Int]? zs # Imagine this doesn't get supplied
  }

  Int len_xs = length(xs) # Returns 3
  Int len_ys = length(ys) # Returns 3
  Int len_zs = length(zs) # Returns 0

[yfarjoun]

right…so

select_first([ maybeArray, []])

will either return maybeArray (if present) or [] (if not) after which you can run length and get 0 when array is not present.

[patmagee]

closing this as it seems the agreed upon solution in the current spec is:

select_first([ maybeArray, []])