|Changes:||Who: Oliver Drotbohm
Why: DATACMNS-1593, DATACMNS-1635 - Overhauled null handling in QuerydslPredicateArgumentResolver.
QuerydslPredicateArgumentResolver now properly handles predicate lookups that result in null values. The semantics of a handler method parameter of type of Querydsl"s Predicate have been tightened to always see a non-null Predicate by default. Users that want to handle the absence of predicates explicitly can opt into seeing null by annotating the parameter with @Nullable or use Optional<Predicate>.
QuerydslPredicateBuilder now consistently returns null in case the original parameter map is entirely empty or consists of only keys with empty value arrays as empty form submissions do. This partially reverts the work of DATACMNS-1168, which moved into the direction of returning a default Predicate value for empty maps in the first place. That however prevents us from producing empty Optionals.
Related tickets: DATACMNS-1168.