Sass syntax error

package.json

@@ -96,6 +96,7 @@
     "postcss-less": "^3.1.0",
     "postcss-markdown": ">=0.36.0",
     "postcss-safe-parser": "^4.0.1",
+    "postcss-sass": "^0.4.4",
     "postcss-scss": "^2.0.0",
     "proxyquire": "^2.1.0",
     "sugarss": "^2.0.0"

patch-postcss.js

@@ -35,7 +35,14 @@ function patchNode (Node) {
 	Node = Node.prototype;
 	const NodeToString = Node.toString;
 	Node.toString = function toString (stringifier) {
-		return NodeToString.call(this, stringifier || this.root().source.syntax);
+		let arg = stringifier;
+		if (!arg) {
+			const source = this.root().source;
+			if (source) {
+				arg = source.syntax;
+			}
+		}
+		return NodeToString.call(this, arg);
 	};
 }
 

test/sass.js

@@ -0,0 +1,29 @@
+"use strict";
+const postcss = require("postcss");
+const expect = require("chai").expect;
+const syntax = require("../")({
+	css: "sass",
+});
+
+describe("sass", () => {
+    it("test", () => {
+        const sass = `
+        $sizes: 40px, 50px, 80px
+        @each $size in $sizes
+            .icon-#{$size}
+                font-size: $size
+        `.trim();
+        return postcss([
+            function (root) {
+                root.nodes.forEach(node => {
+                    node.toString();
+                });
+            }
+        ]).process(sass, {
+            syntax,
+            from: 'style.sass',
+        }).then(result => {
+            expect(result.css).to.equal(sass);
+        });
+    });
+})