Version:
- nette/di: master|3.0.2
- nette/schema: 1.0.2
- nette/application: 3.0.3
The exception
Nette\DI\InvalidConfigurationException
The option 'application › mapping › _prevent_merging' expects to be string or array, bool given.

I believe the Schema is trying to validate _prevent_merging => true as one of the mapping options, which should not be the case.
The configuration
application:
errorPresenter: Error
mapping!:
*: App\*Module\Presenters\*Presenter