Hi!

When using PATCH for objects that use @JsonAnySetter for deserialization and therefore don't have a corresponding property in MappedProperties, DomainObjectReader#doMerge fails. This used to work in previous versions of this class, when

if (!mappedProperties.hasPersistentPropertyForField(fieldName))

was used (without removing the field from deserialization, see changes in commit and commit ). Now

if (!mappedProperties.isWritableProperty(fieldName)) {

checks whether the property is writable (which is an improvement). But this also returns true if the class to merge contains an @JsonAnySetter. This means that the following call

PersistentProperty<?> property = mappedProperties.getPersistentProperty(fieldName);

returns null and the call after this

Optional<Object> rawValue = Optional.ofNullable(accessor.getProperty(property));

Throws the error.

The solution IMHO is a simple null check before the accessor.getProperty call like

if (property == null) {
  continue;
}

This lets @JsonAnySetter handle the further deserialization, as I understand was the intention in previous versions and should be now.

I confirmed this fix with a test case, see referenced pull request.