diff --git a/hugegraph-api/src/main/java/com/baidu/hugegraph/api/auth/AccessAPI.java b/hugegraph-api/src/main/java/com/baidu/hugegraph/api/auth/AccessAPI.java
index 7bd593393b..ac41871a15 100644
--- a/hugegraph-api/src/main/java/com/baidu/hugegraph/api/auth/AccessAPI.java
+++ b/hugegraph-api/src/main/java/com/baidu/hugegraph/api/auth/AccessAPI.java
@@ -149,6 +149,8 @@ public void delete(@Context GraphManager manager,
                        @PathParam("id") String id) {
         LOG.debug("Graph [{}] delete access: {}", graph, id);
 
+        @SuppressWarnings("unused") // just check if the graph exists
+        HugeGraph g = graph(manager, graph);
         try {
             manager.userManager().deleteAccess(UserAPI.parseId(id));
         } catch (NotFoundException e) {
diff --git a/hugegraph-api/src/main/java/com/baidu/hugegraph/api/auth/BelongAPI.java b/hugegraph-api/src/main/java/com/baidu/hugegraph/api/auth/BelongAPI.java
index efff34862f..8aa02ef06c 100644
--- a/hugegraph-api/src/main/java/com/baidu/hugegraph/api/auth/BelongAPI.java
+++ b/hugegraph-api/src/main/java/com/baidu/hugegraph/api/auth/BelongAPI.java
@@ -148,6 +148,8 @@ public void delete(@Context GraphManager manager,
                        @PathParam("id") String id) {
         LOG.debug("Graph [{}] delete belong: {}", graph, id);
 
+        @SuppressWarnings("unused") // just check if the graph exists
+        HugeGraph g = graph(manager, graph);
         try {
             manager.userManager().deleteBelong(UserAPI.parseId(id));
         } catch (NotFoundException e) {
diff --git a/hugegraph-api/src/main/java/com/baidu/hugegraph/api/auth/GroupAPI.java b/hugegraph-api/src/main/java/com/baidu/hugegraph/api/auth/GroupAPI.java
index acbc494414..262ee00e10 100644
--- a/hugegraph-api/src/main/java/com/baidu/hugegraph/api/auth/GroupAPI.java
+++ b/hugegraph-api/src/main/java/com/baidu/hugegraph/api/auth/GroupAPI.java
@@ -134,6 +134,8 @@ public void delete(@Context GraphManager manager,
                        @PathParam("id") String id) {
         LOG.debug("Graph [{}] delete group: {}", graph, id);
 
+        @SuppressWarnings("unused") // just check if the graph exists
+        HugeGraph g = graph(manager, graph);
         try {
             manager.userManager().deleteGroup(IdGenerator.of(id));
         } catch (NotFoundException e) {
diff --git a/hugegraph-api/src/main/java/com/baidu/hugegraph/api/auth/TargetAPI.java b/hugegraph-api/src/main/java/com/baidu/hugegraph/api/auth/TargetAPI.java
index 3c3385f56d..47ea5e710f 100644
--- a/hugegraph-api/src/main/java/com/baidu/hugegraph/api/auth/TargetAPI.java
+++ b/hugegraph-api/src/main/java/com/baidu/hugegraph/api/auth/TargetAPI.java
@@ -134,6 +134,9 @@ public void delete(@Context GraphManager manager,
                        @PathParam("graph") String graph,
                        @PathParam("id") String id) {
         LOG.debug("Graph [{}] delete target: {}", graph, id);
+
+        @SuppressWarnings("unused") // just check if the graph exists
+        HugeGraph g = graph(manager, graph);
         try {
             manager.userManager().deleteTarget(UserAPI.parseId(id));
         } catch (NotFoundException e) {
diff --git a/hugegraph-api/src/main/java/com/baidu/hugegraph/api/auth/UserAPI.java b/hugegraph-api/src/main/java/com/baidu/hugegraph/api/auth/UserAPI.java
index a1e675eee3..5199a79fa1 100644
--- a/hugegraph-api/src/main/java/com/baidu/hugegraph/api/auth/UserAPI.java
+++ b/hugegraph-api/src/main/java/com/baidu/hugegraph/api/auth/UserAPI.java
@@ -136,6 +136,8 @@ public String role(@Context GraphManager manager,
                        @PathParam("id") String id) {
         LOG.debug("Graph [{}] get user role: {}", graph, id);
 
+        @SuppressWarnings("unused") // just check if the graph exists
+        HugeGraph g = graph(manager, graph);
         HugeUser user = manager.userManager().getUser(IdGenerator.of(id));
         return manager.userManager().rolePermission(user).toJson();
     }
@@ -149,6 +151,8 @@ public void delete(@Context GraphManager manager,
                        @PathParam("id") String id) {
         LOG.debug("Graph [{}] delete user: {}", graph, id);
 
+        @SuppressWarnings("unused") // just check if the graph exists
+        HugeGraph g = graph(manager, graph);
         try {
             manager.userManager().deleteUser(IdGenerator.of(id));
         } catch (NotFoundException e) {
diff --git a/hugegraph-api/src/main/java/com/baidu/hugegraph/api/graph/BatchAPI.java b/hugegraph-api/src/main/java/com/baidu/hugegraph/api/graph/BatchAPI.java
index 3343f06233..ebc54be66e 100644
--- a/hugegraph-api/src/main/java/com/baidu/hugegraph/api/graph/BatchAPI.java
+++ b/hugegraph-api/src/main/java/com/baidu/hugegraph/api/graph/BatchAPI.java
@@ -148,7 +148,7 @@ protected void updateExistElement(HugeGraph g,
             } else if (oldElement.property(key).isPresent() &&
                        newElement.properties.get(key) == null) {
                 // If new property is null & old is present, use old property
-                newElement.properties.put(key, oldElement.property(key).value());
+                newElement.properties.put(key, oldElement.value(key));
             }
         }
     }