diff --git a/hugegraph-core/src/main/java/com/baidu/hugegraph/backend/query/ConditionQueryFlatten.java b/hugegraph-core/src/main/java/com/baidu/hugegraph/backend/query/ConditionQueryFlatten.java
index b2cc65eee7..b33d6d3089 100644
--- a/hugegraph-core/src/main/java/com/baidu/hugegraph/backend/query/ConditionQueryFlatten.java
+++ b/hugegraph-core/src/main/java/com/baidu/hugegraph/backend/query/ConditionQueryFlatten.java
@@ -505,6 +505,10 @@ private static class Relations extends LinkedHashSet<Relation> {
 
         private static final long serialVersionUID = -2110811280408887334L;
 
+        public Relations() {
+            super();
+        }
+
         public static Relations of(Relation... relations) {
             Relations rs = new Relations();
             rs.addAll(Arrays.asList(relations));