added missed throws tags in phpdoc for methods

This is a commit to make PhpStorm happy. It claims about missed throws tags in some method of this class. 

Also deleted the `@example` tag at the beginning, cause i can't see that file anywhere. Let me know if it should be kept there.
these are not needed, this is just your IDE missunderstanding the meaning of the code, there is a catch -> rollback -> re throw many places, but this does not mean you'll get a generic Exception.