SingletonPlugin won't throw exception in strict mode if no system uses the component

[acanthite1855]

The doc states, that SingletonPlugin throws exception when an entity enters the world with a @Singleton component.

I made a singleton component, but have not yet added systems that use it (e.g. that want to inject the component into the field). Then I tried to create an entity with the component. I expected it to throw exception, but it worked fine. Here is a kotlin snippet:

@Singleton
class GameMapComponent {
    private val map: GameMap
}

// ...
world = World(WorldConfigurationBuilder()
	.with(SingletonPlugin()) // no other systems added
	.build())

val entity = world.create()
val mapComponent = world
   .getMapper(GameMapComponent::class.java)
   .create(entity)