DATAMONGO-497 - Fixed reading of empty collections.

Reading an empty collection always returned a HashSet assuming the returned value would be converted into the assigned properties value later on. However the method should rather return the correct type already which we do now by invoking the potential conversion.

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/MappingMongoConverter.java

@@ -720,11 +720,12 @@ public class MappingMongoConverter extends AbstractMongoConverter implements App
 
 		Assert.notNull(targetType);
 
+		Class<?> collectionType = targetType.getType();
+
 		if (sourceValue.isEmpty()) {
-			return new HashSet<Object>();
+			return getPotentiallyConvertedSimpleRead(new HashSet<Object>(), collectionType);
 		}
 
-		Class<?> collectionType = targetType.getType();
 		collectionType = Collection.class.isAssignableFrom(collectionType) ? collectionType : List.class;
 
 		Collection<Object> items = targetType.getType().isArray() ? new ArrayList<Object>() : CollectionFactory

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/convert/MappingMongoConverterUnitTests.java

@@ -1252,6 +1252,18 @@ public class MappingMongoConverterUnitTests {
 		assertThat(values, is(arrayWithSize(2)));
 	}
 
+	/**
+	 * @see DATAMONGO-497
+	 */
+	@Test
+	public void readsEmptyCollectionIntoConstructorCorrectly() {
+
+		DBObject source = new BasicDBObject("attributes", new BasicDBList());
+
+		TypWithCollectionConstructor result = converter.read(TypWithCollectionConstructor.class, source);
+		assertThat(result.attributes, is(notNullValue()));
+	}
+
 	private static void assertSyntheticFieldValueOf(Object target, Object expected) {
 
 		for (int i = 0; i < 10; i++) {
@@ -1440,6 +1452,15 @@ public class MappingMongoConverterUnitTests {
 		Long innerId;
 	}
 
+	static class TypWithCollectionConstructor {
+
+		List<Attribute> attributes;
+
+		public TypWithCollectionConstructor(List<Attribute> attributes) {
+			this.attributes = attributes;
+		}
+	}
+
 	private class LocalDateToDateConverter implements Converter<LocalDate, Date> {
 
 		public Date convert(LocalDate source) {