Throw exception when block type is not set

Rather than Fatal Error,

Fixes #174 

[short description]:

__Tasks:__

- [ x ] test coverage
- [ ] gather feedback for my changes

__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | yes 
| Fixed tickets | [ #174 
| BC Breaks     | NO 
| Doc           | N.A