lib/less/js/lib/less/tree/operation.js in less-2.3.0 vs lib/less/js/lib/less/tree/operation.js in less-2.3.1

@@ -15,9 +15,14 @@
         } else {
             throw { name: "OperationError",
                     message: "Can't substract or divide a color from a number" };
         }
     }
+    if (!a.operate) {
+        throw { name: "OperationError",
+                message: "Operation on an invalid type" };
+    }
+
     return a.operate(this.op, b);
 };
 
 tree.operate = function (op, a, b) {
     switch (op) {