Regression in latest version with config
Installed the latest version and got some issues regarding config it expects that exists
```
backend_config:
...
+ search_system: ''
+ language_fallback: true
+ max_distance: null
+ alpha: null
+ distance: null
```
without those its pritty broken
also, the form with invalid credentials is breaking the later options - so new installs also misses the config
display_extenders key-value is also in invalid format
issue