Issue: It is not possible to use function without return when
       matching steps, resulting in a lot of Nil only error
       returns.

Fix: Allows to provide empty result function by correctly matching
     reflect Calls on step Handler.
     When nothing is returned by the Handler, it will return
     nil as if errors was nil.

Add tests for panic in test_context initialization.

Made as independ commit so it can be rollbacked.