SHA-1: f1f991c475660c799b55bd625a112d2005d6102e
* Fix a bug that overwrite an item list when it has only one client
- The previous fix that using a 'singleItem' flag does not reflect the original author's intention.
   - If 'createClient' method is invoked, there is a single client instance, and the 'item' is obviously provided. (so the first branch should check item is not null)
   - If 'createClients' method is invoked, a single client or multiple clients are possible, and the 'item' is omitted. (instead, items are provided as a form of array)
   - As a single client with multiple items is created by 'createClients' method, the second method branch must be followed. In the previous version, it follows the first method branch.