Fix circular json error

node_modules/c9/urls.js

@@ -34,7 +34,8 @@ plugin.getBaseUrl = function(req, sourceBaseUrlPattern, targetBaseUrlPattern) {
         || req.host
         || req.url && req.url.replace(/^https?:\/\/([^/]*).*/, "$1")
         || req;
-    assert(typeof sourceHost === "string", "Not a valid request object: " + JSON.stringify(req));
+    if (typeof sourceHost !== "string")
+        throw new Error("Not a valid request object: " + req);
 
     var sourceHostMatcher = sourceBaseUrlPattern
         .replace(/^https?:\/\//, "")