At least one configuration property that did not exist in Search 5 should be provided explicitly by the user in order for Search 6 to bootstrap successfully.
This way, we will ensure that every user migrating from Search 5 to Search 6 will think about updating his configuration.
The most obvious choice would be to require users to set their backend type explicitly; the minimal configuration file would then be:
Or something similar.
We should add tests to be sure bootstrapping with Search 5 configuration properties actually fails.