remove variables before toCSS

lib/less/to-css-visitor.js

@@ -10,10 +10,12 @@
             return this._visitor.visit(root);
         },
 
-        //visitRule: function (ruleNode, visitArgs) {
-        //    visitArgs.visitDeeper = false;
-        //    return ruleNode;
-        //},
+        visitRule: function (ruleNode, visitArgs) {
+            if (ruleNode.variable) {
+                return [];
+            }
+            return ruleNode;
+        },
 
         visitComment: function (commentNode, visitArgs) {
             if (commentNode.isSilent(this._env)) {

lib/less/tree/ruleset.js

@@ -203,13 +203,13 @@ tree.Ruleset.prototype = {
                     rules.push(rule.toCSS(env));
                 }
             } else {
-                if (rule.toCSS && !rule.variable) {
+                if (rule.toCSS) {
                     if (this.firstRoot && rule instanceof tree.Rule) {
                         throw { message: "properties must be inside selector blocks, they cannot be in the root.",
                             index: rule.index, filename: rule.currentFileInfo ? rule.currentFileInfo.filename : null};
                     }
                     rules.push(rule.toCSS(env));
-                } else if (rule.value && !rule.variable) {
+                } else if (rule.value) {
                     rules.push(rule.value.toString());
                 }
             }