54e105
@@ -20,6 +20,7 @@
import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
@@ -470,7 +471,6 @@
public class MappingMongoConverter extends AbstractMongoConverter implements App
 	 * 
 	 * @param collection must not be {@literal null}.
 	 * @param property must not be {@literal null}.
-	 * 
 	 * @return
 	 */
 	protected DBObject createCollection(Collection<?> collection, MongoPersistentProperty property) {
@@ -721,7 +721,7 @@
public class MappingMongoConverter extends AbstractMongoConverter implements App
 		Assert.notNull(targetType);
 
 		if (sourceValue.isEmpty()) {
-			return Collections.emptySet();
+			return new HashSet<Object>();
 		}
 
 		Class<?> collectionType = targetType.getType();
