properly recognize arglist of null as null

src/args.rs

@@ -10,10 +10,10 @@ use crate::{
     {Cow, Token},
 };
 
-#[derive(Debug, Clone, Eq, PartialEq)]
+#[derive(Debug, Clone)]
 pub(crate) struct FuncArgs(pub Vec<FuncArg>);
 
-#[derive(Debug, Clone, Eq, PartialEq)]
+#[derive(Debug, Clone)]
 pub(crate) struct FuncArg {
     pub name: Identifier,
     pub default: Option<Vec<Token>>,
@@ -89,7 +89,7 @@ impl CallArgs {
                 .iter()
                 .map(|a| {
                     span = span.merge(a.span);
-                    Ok(a.node.to_css_string(a.span)?)
+                    a.node.to_css_string(a.span)
                 })
                 .collect::<SassResult<Vec<Cow<'static, str>>>>()?
                 .join(", "),

src/parse/value/parse.rs

@@ -207,8 +207,7 @@ impl<'a> Parser<'a> {
 
         let lower = s.to_ascii_lowercase();
 
-        if lower == "progid" && self.toks.peek().is_some() && self.toks.peek().unwrap().kind == ':'
-        {
+        if lower == "progid" && matches!(self.toks.peek(), Some(Token { kind: ':', .. })) {
             s = lower;
             self.toks.next();
             s.push(':');

src/value/mod.rs

@@ -112,12 +112,9 @@ impl Value {
             Value::Null => true,
             Value::String(i, QuoteKind::None) if i.is_empty() => true,
             Value::List(v, _, Brackets::Bracketed) if v.is_empty() => false,
-            Value::List(v, ..) => v
-                .iter()
-                .map(Value::is_null)
-                .collect::<Vec<bool>>()
-                .into_iter()
-                .all(|f| f),
+            Value::List(v, ..) => v.iter().map(Value::is_null).all(|f| f),
+            Value::ArgList(v, ..) if v.is_empty() => false,
+            Value::ArgList(v, ..) => v.iter().map(|v| v.node.is_null()).all(|f| f),
             _ => false,
         }
     }

tests/arglist.rs

@@ -73,3 +73,24 @@ test!(
     }",
     "a {\n  color: (1,);\n}\n"
 );
+error!(
+    empty_arglist_is_error,
+    "@function foo($a...) {
+        @return $a;
+    }
+
+    a {
+        color: foo();
+    }",
+    "Error: () isn't a valid CSS value."
+);
+test!(
+    arglist_of_only_null_is_null,
+    "@function foo($a...) {
+        @return $a;
+    }
+    a {
+        color: foo(null, null);
+    }",
+    ""
+);