DATAREST-1260 - Tweaked DomainObjectReader to support immutable entities.

DomainObjectReader now aborts the recursive merges in case it encounters an entity that's described as @Immutable (just introduced in Spring Data Commons).

Fixed some generics and removed DomainObjectMerger as it's unused.

Related ticket: DATACMNS-1322.

spring-data-rest-webmvc/src/test/java/org/springframework/data/rest/webmvc/json/DomainObjectReaderUnitTests.java

@@ -23,6 +23,7 @@ import static org.mockito.Mockito.*;
 
 import lombok.AllArgsConstructor;
 import lombok.EqualsAndHashCode;
+import lombok.Getter;
 import lombok.NoArgsConstructor;
 import lombok.RequiredArgsConstructor;
 import lombok.Value;
@@ -51,6 +52,7 @@ import org.mockito.Mock;
 import org.mockito.junit.MockitoJUnitRunner;
 import org.springframework.data.annotation.CreatedDate;
 import org.springframework.data.annotation.Id;
+import org.springframework.data.annotation.Immutable;
 import org.springframework.data.annotation.ReadOnlyProperty;
 import org.springframework.data.annotation.Reference;
 import org.springframework.data.annotation.Transient;
@@ -734,11 +736,13 @@ public class DomainObjectReaderUnitTests {
 		List<SampleEnum> enums = new ArrayList<SampleEnum>();
 	}
 
-	@Value
+	@EqualsAndHashCode
+	@AllArgsConstructor
 	static class SampleWithReference {
-		@Reference List<Nested> nested;
+		private @Getter @Reference List<Nested> nested;
 	}
 
+	@Immutable
 	@Value
 	static class Nested {
 		int x, y;