Check for null and undefined explicitly

Author: buremba

rakam.js

@@ -636,8 +636,8 @@ Rakam.prototype.setUserId = function (userId) {
         var previousUserId = this.options.userId;
         this.options.userId = (userId !== undefined && userId !== null && ('' + userId)) || null;
 
-        if (userId !== null && userId !== undefined && ((this._eventId > 0 && previousUserId === null) ||
-            (previousUserId !== null && this.deviceIdCreatedAt !== undefined))) {
+        if (userId !== null && userId !== undefined && ((this._eventId > 0 && (previousUserId === null || previousUserId === undefined)) ||
+            (previousUserId !== null && previousUserId !== undefined && this.deviceIdCreatedAt !== undefined))) {
             var _this = this;
             this.User()._merge(previousUserId, this.deviceIdCreatedAt, function () {
                 _this.deviceIdCreatedAt = undefined;