Do not accept empty condition list if unnecessary

[joorei]

RepositoryInterface::assertMatchingEntity accepts an empty list of conditions, which implies the method could perform any logic on such input. But it will in fact always simply return without an exception.

This distinction is important to set its purpose apart from FilterableTypeInterface::assertMatchingEntity, which correctly accepts an empty list of conditions, as those are optional and the method may additionally apply internal conditions defined by the implementation (e.g. such inheriting from AbstractResourceType).