title: Spring Data REST updates null properties on PATCH (when it shouldn't)
body: <p>I am sending a PATCH request with null values in some properties of the entity and I see that the fields are updated in the database whereas according to spec they shouldn't (partial update). Trying to understand what's going on I see that the DomainObjectMerger is instantiated as a @Bean but its merge method never used (no references found and in debug mode breakpoint is never fired). Could someone explain how and when is the DomainObjectMerger used?</p>
  
  <p>EDIT: I created a sample project with a failing test. The test tries to PATCH an entity passing null as a password and expects the password to not have been affected. But it fails because the password is now null in the database</p>
  
  <p><a href="https://github.com/otinanism/demo-rest-data" rel="nofollow noreferrer">https://github.com/otinanism/demo-rest-data</a></p>