Fix empty belongs to links generation to be nil

Was: 
![image](https://cloud.githubusercontent.com/assets/464900/3249149/e3c7aa06-f195-11e3-89af-b9c6040f29dd.png)

Now: 
![image](https://cloud.githubusercontent.com/assets/464900/3249150/e858e648-f195-11e3-9b96-002e1e7fc7c2.png)