Unquote empty string is null

src/builtin/string.rs

@@ -45,7 +45,7 @@ pub(crate) fn register(f: &mut BTreeMap<String, Builtin>) {
     decl!(f "unquote", |args, _| {
         max_args!(args, 1);
         match arg!(args, 0, "string").eval() {
-            Value::Ident(i, QuoteKind::None) if i.is_empty() => Ok(Value::Null),
+            Value::Ident(i, _) if i.is_empty() => Ok(Value::Null),
             i @ Value::Ident(..) => Ok(i.unquote()),
             v => Err(format!("$string: {} is not a string.", v).into()),
         }

tests/strings.rs

@@ -93,6 +93,11 @@ test!(
     "a {\n  color: str-length(cde);\n}\n",
     "a {\n  color: 3;\n}\n"
 );
+test!(
+    unquote_empty_string_is_null,
+    "a {\n  color: unquote('');\n}\n",
+    ""
+);
 // blocked on refactoring how function-call args are parsed
 // right now, whitespace is eaten between idents with no
 // regard for quotes