DATAJDBC-374 - Polishing.

Clarified the effects of collections on nullable embedded entities.

Original pull request: #154.

spring-data-jdbc/src/main/java/org/springframework/data/jdbc/core/convert/BasicJdbcConverter.java

@@ -378,11 +378,15 @@ public class BasicJdbcConverter extends BasicRelationalConverter implements Jdbc
 
 			ReadingContext<?> newContext = extendBy(property);
 
-			if(OnEmpty.USE_EMPTY.equals(property.findAnnotation(Embedded.class).onEmpty())) {
+			if(shouldCreateEmptyEmbeddedInstance(property) || newContext.hasInstanceValues(idValue)) {
 				return newContext.createInstanceInternal(idValue);
 			}
 
-			return newContext.hasInstanceValues(idValue) ? newContext.createInstanceInternal(idValue) : null;
+			return null;
+		}
+
+		private boolean shouldCreateEmptyEmbeddedInstance(RelationalPersistentProperty property) {
+			return OnEmpty.USE_EMPTY.equals(property.findAnnotation(Embedded.class).onEmpty());
 		}
 
 		private boolean hasInstanceValues(@Nullable Object idValue) {

src/main/asciidoc/jdbc.adoc

@@ -332,6 +332,9 @@ public class MyEntity {
 <1> Shortcut for `@Embedded(onEmpty = USE_NULL)`.
 ====
 
+Embedded entities containing a `Collection` or a `Map` will always be considered non empty since they will at least contain the empty collection or map.
+Such an entity will therefore never be `null` even when using @Embedded(onEmpty = USE_NULL).
+
 [[jdbc.entity-persistence.state-detection-strategies]]
 === Entity State Detection Strategies