[PATCH 1/2] stk: Constraint the appearance of empty item

[Denis Kenzior]

Hi Yang,

> If empty item turns out, it must be the only item in the list.
> So the following situations are deemed as invalid:
> 1. Two empty items
> 2. Valid item + empty item
> 3. empty + valid item

Both have been applied, thanks.

Regards,
-Denis