Make none spreadable

src/eval/mod.rs

@@ -412,6 +412,7 @@ impl Eval for CallArgs {
                     });
                 }
                 CallArg::Spread(expr) => match expr.eval(ctx)? {
+                    Value::None => {}
                     Value::Array(array) => {
                         items.extend(array.into_iter().map(|value| Arg {
                             span,

tests/typ/code/spread.typ

@@ -50,6 +50,13 @@
   test(tostr(a: 1, ..more, b: 2), "(a: 1, c: 3, d: 4, b: 2)")
 }
 
+---
+// None is spreadable.
+#let f() = none
+#f(..none)
+#f(..if false {})
+#f(..for x in () [])
+
 ---
 // Error: 8-14 cannot spread string
 #min(.."nope")