Fix test; Pass all tests

dust-lang/src/abstract_tree/value_node.rs

@@ -67,7 +67,11 @@ impl AbstractNode for ValueNode {
     ) -> Result<(), ValidationError> {
         if let ValueNode::List(list) = self {
             let mut items = list.into_iter();
-            let first_item = items.next().unwrap();
+            let first_item = if let Some(item) = items.next() {
+                item
+            } else {
+                return Ok(());
+            };
             let first_item_type = if let Some(r#type) = first_item.expected_type(context)? {
                 r#type
             } else {

dust-lang/tests/values.rs

@@ -87,11 +87,11 @@ fn string() {
 #[test]
 fn list() {
     assert_eq!(
-        interpret("test", "[1, 2, 'foobar']"),
+        interpret("test", "[1, 2, 3]"),
         Ok(Some(Value::list(vec![
             Value::integer(1),
             Value::integer(2),
-            Value::string("foobar".to_string()),
+            Value::integer(3),
         ])))
     );
 }