dont crash if data.username is undefined, dont set username to empty value

src/user/profile.js

@@ -57,6 +57,9 @@ module.exports = function(User) {
 			}
 
 			function isUsernameAvailable(next) {
+				if (!data.username) {
+					return next();
+				}
 				User.getUserFields(uid, ['username', 'userslug'], function(err, userData) {
 
 					var userslug = utils.slugify(data.username);
@@ -177,6 +180,9 @@ module.exports = function(User) {
 	}
 
 	function updateUsername(uid, newUsername, callback) {
+		if (!newUsername) {
+			return callback();
+		}
 		User.getUserFields(uid, ['username', 'userslug'], function(err, userData) {
 			function update(field, object, value, callback) {
 				async.parallel([