Fix #177 (Null values aren't serialized correctly)

Fix by serializing null and undefined values to blank strings. This is what jQuery also does.

Author: prashantsharmain

ajax-test.js

@@ -171,3 +171,18 @@ QUnit.asyncTest("crossDomain is true for relative requests", function(){
 		start();
 	});
 });
+
+if (__dirname !== '/') {
+	QUnit.asyncTest("correctly serializes null and undefined values (#177)", function () {
+		ajax({
+			type: "get",
+			url: __dirname + "/test-result.txt",
+			data: {
+				foo: null
+			}
+		}).then(function (resp) {
+			QUnit.equal(resp.message, "VALUE");
+			start();
+		});
+	});
+}

ajax.js

@@ -73,9 +73,11 @@ $._xhrResp = function (xhr, options) {
 	}
 };
 $._formData = function (o) {
-	var kvps = [], regEx = /%20/g;
+	var kvps = [], regEx = /%20/g, val;
 	for (var k in o) {
-		kvps.push(encodeURIComponent(k).replace(regEx, "+") + "=" + encodeURIComponent(o[k].toString()).replace(regEx, "+"));
+		val = o[k];
+		val = typeof val === "undefined" || val === null ? "" : val;
+		kvps.push(encodeURIComponent(k).replace(regEx, "+") + "=" + encodeURIComponent(val.toString()).replace(regEx, "+"));
 	}
 	return kvps.join('&');
 };