[midPoint-git] [Evolveum/midpoint] 069017: Allow empty values for identity recovery

[mederly]

  Branch: refs/heads/feature/mid-9233
  Home:   https://github.com/Evolveum/midpoint
  Commit: 069017556cffdce243c96b46ca070552c45370c4
      https://github.com/Evolveum/midpoint/commit/069017556cffdce243c96b46ca070552c45370c4
  Author: Pavol Mederly <mederly at evolveum.com>
  Date:   2023-10-12 (Thu, 12 Oct 2023)

  Changed paths:
    M infra/schema/src/main/java/com/evolveum/midpoint/schema/CorrelatorDiscriminator.java
    M model/authentication-impl/src/main/java/com/evolveum/midpoint/authentication/impl/module/authentication/token/CorrelationVerificationToken.java
    M model/model-api/src/main/java/com/evolveum/midpoint/model/api/correlator/CorrelatorContext.java
    M model/model-impl/src/main/java/com/evolveum/midpoint/model/impl/correlation/CorrelatorContextCreator.java
    M model/model-impl/src/main/java/com/evolveum/midpoint/model/impl/correlator/BaseCorrelator.java
    M model/model-impl/src/main/java/com/evolveum/midpoint/model/impl/correlator/items/CorrelationItem.java
    M model/model-impl/src/main/java/com/evolveum/midpoint/model/impl/correlator/items/ItemsCorrelator.java
    M model/model-impl/src/test/java/com/evolveum/midpoint/model/impl/correlator/correlation/TestCorrelators.java

  Log Message:
  -----------
  Allow empty values for identity recovery

Identity recovery feature did not supported empty values for individual
properties. (Like missing middle name.)

This commit fixes that by:
1. extending items correlator to allow null values (meaning the
   candidate has to have null value in the respective item as well);
2. adapting the GUI to treat empty strings as null values.

Note that the correlators are adapted only for the identity recovery
feature. The synchronization-related correlation still does not allow
null values. This is to avoid unexpected last-minute functionality
changes.

This resolves MID-9233.