Some optionals fixed

## What? Why?
With beta6 some methods returned not optionals but with beta7 these returned items turned into optionals

## What should be tested?
The library works

## Related tasks? 
No related task
![image](http://media.giphy.com/media/y9VV9tmOwfDxu/giphy.gif)

Take a look to the lines above. There is an if check before doing this unwrap. Is this what you mean?:

```swift
if context == nil && NSManagedObjectContext.defaultContext() != nil {
            context = NSManagedObjectContext.defaultContext()!
        }
        else {
            assert(true, "Context should be passed or default should be set")
        }
        var error: NSError?
```