BaseModel.search might return nil

I've seen this error in airbrake a couple of times.

![skarmavbild 2013-11-06 kl 22 38 50](https://f.cloud.github.com/assets/220827/1486950/ed1150a4-472b-11e3-8cd4-d9f3a8a27e92.png)

I'm not sure why, but 1 out of 10^4 times (or something similar) `BaseModel.search` returns nil.

This PR will fix this error. 

All specs passes.