Since Spring 4.1, a CacheResolver may be configured to customize the way
the cache(s) to use for a given cache operation are retrieved. Since a
CacheResolver implementation may not use the cache names information at
all, this attribute has been made optional.
However, a fix was still applied, preventing a Cache operation without a
cache name to be defined properly. We now allow this valid use case.
Issue: SPR-13081
08c032d9fd