int sum(int[]? arr) {
    var acc = 0;
    if? (int[] a = arr) {
      for(var i = 0; i < length(a); i = i+1;) {
        acc = acc + a[i];
      }
    } 
    return acc;
}


int program (int argc, string[] argv) {
  var a1 = new int[]{1, 2, 3, 4};
  var a2 = int[] null;
  var x = sum(a1) + sum(a2);
  return x;
}