diff --git a/apollo-audit/apollo-audit-impl/src/main/java/com/ctrip/framework/apollo/audit/component/ApolloAuditLogApiJpaImpl.java b/apollo-audit/apollo-audit-impl/src/main/java/com/ctrip/framework/apollo/audit/component/ApolloAuditLogApiJpaImpl.java
index d8489c3b2bd..0ff85c3e300 100644
--- a/apollo-audit/apollo-audit-impl/src/main/java/com/ctrip/framework/apollo/audit/component/ApolloAuditLogApiJpaImpl.java
+++ b/apollo-audit/apollo-audit-impl/src/main/java/com/ctrip/framework/apollo/audit/component/ApolloAuditLogApiJpaImpl.java
@@ -95,7 +95,7 @@ public void appendDataInfluence(String entityName, String entityId, String field
   @Override
   public void appendDataInfluences(List<Object> entities, Class<?> beanDefinition) {
     String tableName = ApolloAuditUtil.getApolloAuditLogTableName(beanDefinition);
-    if (Objects.isNull(tableName) || tableName.equals("")) {
+    if (Objects.isNull(tableName) || Objects.equals(tableName, "")) {
       return;
     }
     List<Field> dataInfluenceFields = ApolloAuditUtil.getAnnotatedFields(
diff --git a/apollo-audit/apollo-audit-impl/src/main/java/com/ctrip/framework/apollo/audit/component/ApolloAuditLogApiNoOpImpl.java b/apollo-audit/apollo-audit-impl/src/main/java/com/ctrip/framework/apollo/audit/component/ApolloAuditLogApiNoOpImpl.java
index 6de5f0a018e..e12e780939b 100644
--- a/apollo-audit/apollo-audit-impl/src/main/java/com/ctrip/framework/apollo/audit/component/ApolloAuditLogApiNoOpImpl.java
+++ b/apollo-audit/apollo-audit-impl/src/main/java/com/ctrip/framework/apollo/audit/component/ApolloAuditLogApiNoOpImpl.java
@@ -21,6 +21,7 @@
 import com.ctrip.framework.apollo.audit.dto.ApolloAuditLogDataInfluenceDTO;
 import com.ctrip.framework.apollo.audit.dto.ApolloAuditLogDetailsDTO;
 import com.ctrip.framework.apollo.audit.dto.ApolloAuditLogDTO;
+import java.util.Collections;
 import java.util.Date;
 import java.util.List;
 
@@ -50,28 +51,28 @@ public void appendDataInfluences(List<Object> entities, Class<?> beanDefinition)
 
   @Override
   public List<ApolloAuditLogDTO> queryLogs(int page, int size) {
-    return null;
+    return Collections.emptyList();
   }
 
   @Override
   public List<ApolloAuditLogDTO> queryLogsByOpName(String opName, Date startDate,
       Date endDate, int page, int size) {
-    return null;
+    return Collections.emptyList();
   }
 
   @Override
   public List<ApolloAuditLogDetailsDTO> queryTraceDetails(String traceId) {
-    return null;
+    return Collections.emptyList();
   }
 
   @Override
   public List<ApolloAuditLogDataInfluenceDTO> queryDataInfluencesByField(String entityName,
       String entityId, String fieldName, int page, int size) {
-    return null;
+    return Collections.emptyList();
   }
 
   @Override
   public List<ApolloAuditLogDTO> searchLogByNameOrTypeOrOperator(String query, int page, int size) {
-    return null;
+    return Collections.emptyList();
   }
 }
diff --git a/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/entity/Audit.java b/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/entity/Audit.java
index 4f2ac566b41..9ec2965d726 100644
--- a/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/entity/Audit.java
+++ b/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/entity/Audit.java
@@ -79,6 +79,7 @@ public void setOpName(String opName) {
     this.opName = opName;
   }
 
+  @Override
   public String toString() {
     return toStringHelper().add("entityName", entityName).add("entityId", entityId)
         .add("opName", opName).add("comment", comment).toString();
diff --git a/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/entity/Cluster.java b/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/entity/Cluster.java
index 3bcb626b8f8..20573407ccc 100644
--- a/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/entity/Cluster.java
+++ b/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/entity/Cluster.java
@@ -78,6 +78,7 @@ public void setComment(String comment) {
     this.comment = comment;
   }
 
+  @Override
   public String toString() {
     return toStringHelper().add("name", name).add("appId", appId)
         .add("parentClusterId", parentClusterId).add("comment", comment).toString();
diff --git a/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/entity/Item.java b/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/entity/Item.java
index f18218b1725..9c5a6802256 100644
--- a/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/entity/Item.java
+++ b/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/entity/Item.java
@@ -99,6 +99,7 @@ public void setType(int type) {
     this.type = type;
   }
 
+  @Override
   public String toString() {
     return toStringHelper().add("namespaceId", namespaceId).add("key", key)
             .add("type", type).add("value", value)
diff --git a/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/entity/Namespace.java b/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/entity/Namespace.java
index bc966c0d66a..846803aeab0 100644
--- a/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/entity/Namespace.java
+++ b/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/entity/Namespace.java
@@ -74,6 +74,7 @@ public void setNamespaceName(String namespaceName) {
     this.namespaceName = namespaceName;
   }
 
+  @Override
   public String toString() {
     return toStringHelper().add("appId", appId).add("clusterName", clusterName)
         .add("namespaceName", namespaceName).toString();
diff --git a/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/entity/Privilege.java b/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/entity/Privilege.java
index d86095f45e8..d3db68574ca 100644
--- a/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/entity/Privilege.java
+++ b/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/entity/Privilege.java
@@ -64,6 +64,7 @@ public void setPrivilType(String privilType) {
     this.privilType = privilType;
   }
 
+  @Override
   public String toString() {
     return toStringHelper().add("namespaceId", namespaceId).add("privilType", privilType)
         .add("name", name).toString();
diff --git a/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/entity/Release.java b/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/entity/Release.java
index 2f33516e3e3..1484d0201f5 100644
--- a/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/entity/Release.java
+++ b/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/entity/Release.java
@@ -123,6 +123,7 @@ public void setAbandoned(boolean abandoned) {
     isAbandoned = abandoned;
   }
 
+  @Override
   public String toString() {
     return toStringHelper().add("name", name).add("appId", appId).add("clusterName", clusterName)
         .add("namespaceName", namespaceName).add("configurations", configurations)
diff --git a/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/entity/ReleaseHistory.java b/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/entity/ReleaseHistory.java
index d387f1cb0ec..e5583432d88 100644
--- a/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/entity/ReleaseHistory.java
+++ b/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/entity/ReleaseHistory.java
@@ -121,6 +121,7 @@ public void setOperationContext(String operationContext) {
     this.operationContext = operationContext;
   }
 
+  @Override
   public String toString() {
     return toStringHelper().add("appId", appId).add("clusterName", clusterName)
         .add("namespaceName", namespaceName).add("branchName", branchName)
diff --git a/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/entity/ServerConfig.java b/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/entity/ServerConfig.java
index 8da6913022f..d7a55d53959 100644
--- a/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/entity/ServerConfig.java
+++ b/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/entity/ServerConfig.java
@@ -77,7 +77,8 @@ public void setCluster(String cluster) {
     this.cluster = cluster;
   }
 
+  @Override
   public String toString() {
-    return toStringHelper().add("key", key).add("value", value).add("comment", comment).toString();
+    return toStringHelper().add("key", key).add("value", value).add("cluster", cluster).add("comment", comment).toString();
   }
 }
diff --git a/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/registry/DatabaseServiceRegistryImpl.java b/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/registry/DatabaseServiceRegistryImpl.java
index 454f779174e..269ee819cab 100644
--- a/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/registry/DatabaseServiceRegistryImpl.java
+++ b/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/registry/DatabaseServiceRegistryImpl.java
@@ -37,11 +37,13 @@ static ServiceRegistry convert(ServiceInstance instance) {
     return serviceRegistry;
   }
 
+  @Override
   public void register(ServiceInstance instance) {
     ServiceRegistry serviceRegistry = convert(instance);
     this.serviceRegistryService.saveIfNotExistByServiceNameAndUri(serviceRegistry);
   }
 
+  @Override
   public void deregister(ServiceInstance instance) {
     ServiceRegistry serviceRegistry = convert(instance);
     this.serviceRegistryService.delete(serviceRegistry);
diff --git a/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/registry/configuration/support/ApolloServiceRegistryProperties.java b/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/registry/configuration/support/ApolloServiceRegistryProperties.java
index 10e285e238f..9238492f1c6 100644
--- a/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/registry/configuration/support/ApolloServiceRegistryProperties.java
+++ b/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/registry/configuration/support/ApolloServiceRegistryProperties.java
@@ -97,6 +97,7 @@ public void setEnabled(boolean enabled) {
     this.enabled = enabled;
   }
 
+  @Override
   public String getServiceName() {
     return serviceName;
   }
diff --git a/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/utils/ReleaseMessageKeyGenerator.java b/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/utils/ReleaseMessageKeyGenerator.java
index b3f7cc22ca6..640ad4ee2e2 100644
--- a/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/utils/ReleaseMessageKeyGenerator.java
+++ b/apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/utils/ReleaseMessageKeyGenerator.java
@@ -21,6 +21,7 @@
 
 import com.ctrip.framework.apollo.core.ConfigConsts;
 import com.google.common.base.Splitter;
+import java.util.Collections;
 import java.util.List;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -42,7 +43,7 @@ public static List<String> messageToList(String message) {
     //message should be appId+cluster+namespace
     if (keys.size() != 3) {
       logger.error("message format invalid - {}", message);
-      return null;
+      return Collections.emptyList();
     }
     return keys;
   }
diff --git a/apollo-biz/src/test/java/com/ctrip/framework/apollo/biz/utils/ReleaseKeyGeneratorTest.java b/apollo-biz/src/test/java/com/ctrip/framework/apollo/biz/utils/ReleaseKeyGeneratorTest.java
index a36a75a2013..a074623e7f6 100644
--- a/apollo-biz/src/test/java/com/ctrip/framework/apollo/biz/utils/ReleaseKeyGeneratorTest.java
+++ b/apollo-biz/src/test/java/com/ctrip/framework/apollo/biz/utils/ReleaseKeyGeneratorTest.java
@@ -23,8 +23,6 @@
 
 import java.util.List;
 import org.junit.Test;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
 
 import java.util.Set;
 import java.util.concurrent.CountDownLatch;
@@ -33,7 +31,6 @@
 import java.util.concurrent.TimeUnit;
 
 import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertNull;
 
 /**
  * @author Jason Song(song_s@ctrip.com)
@@ -80,7 +77,8 @@ public void testMessageToList() {
 
     message = "appId+cluster";
     keys = ReleaseMessageKeyGenerator.messageToList(message);
-    assertNull(keys);
+    assert keys != null;
+    assertEquals(0, keys.size());
   }
 
   private Runnable generateReleaseKeysTask(Namespace namespace, Set<String> releaseKeys,
diff --git a/apollo-common/src/main/java/com/ctrip/framework/apollo/common/datasource/ApolloDataSourceScriptDatabaseInitializerFactory.java b/apollo-common/src/main/java/com/ctrip/framework/apollo/common/datasource/ApolloDataSourceScriptDatabaseInitializerFactory.java
index 74106334df7..ad3a1b8cbef 100644
--- a/apollo-common/src/main/java/com/ctrip/framework/apollo/common/datasource/ApolloDataSourceScriptDatabaseInitializerFactory.java
+++ b/apollo-common/src/main/java/com/ctrip/framework/apollo/common/datasource/ApolloDataSourceScriptDatabaseInitializerFactory.java
@@ -20,6 +20,7 @@
 import java.security.CodeSource;
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.Collections;
 import java.util.List;
 import javax.sql.DataSource;
 import org.springframework.boot.jdbc.DataSourceBuilder;
@@ -101,7 +102,7 @@ private static List<String> resolveLocations(Collection<String> locations,
   private static Collection<String> convertRepositoryLocations(Collection<String> locations,
       DataSource dataSource) {
     if (CollectionUtils.isEmpty(locations)) {
-      return null;
+      return Collections.emptyList();
     }
     String repositoryDir = findRepositoryDirectory();
     String suffix = findSuffix(dataSource);
diff --git a/apollo-common/src/main/java/com/ctrip/framework/apollo/common/entity/App.java b/apollo-common/src/main/java/com/ctrip/framework/apollo/common/entity/App.java
index cef034aac5e..d487ef2f8f3 100644
--- a/apollo-common/src/main/java/com/ctrip/framework/apollo/common/entity/App.java
+++ b/apollo-common/src/main/java/com/ctrip/framework/apollo/common/entity/App.java
@@ -111,6 +111,7 @@ public void setOwnerName(String ownerName) {
     this.ownerName = ownerName;
   }
 
+  @Override
   public String toString() {
     return toStringHelper().add("name", name).add("appId", appId)
         .add("orgId", orgId)
diff --git a/apollo-common/src/main/java/com/ctrip/framework/apollo/common/entity/AppNamespace.java b/apollo-common/src/main/java/com/ctrip/framework/apollo/common/entity/AppNamespace.java
index 251c3737b90..b85edebeecc 100644
--- a/apollo-common/src/main/java/com/ctrip/framework/apollo/common/entity/AppNamespace.java
+++ b/apollo-common/src/main/java/com/ctrip/framework/apollo/common/entity/AppNamespace.java
@@ -107,6 +107,7 @@ public void setFormat(String format) {
     this.format = format;
   }
 
+  @Override
   public String toString() {
     return toStringHelper().add("name", name).add("appId", appId).add("comment", comment)
         .add("format", format).add("isPublic", isPublic).toString();
diff --git a/apollo-common/src/main/java/com/ctrip/framework/apollo/common/entity/BaseEntity.java b/apollo-common/src/main/java/com/ctrip/framework/apollo/common/entity/BaseEntity.java
index 75b3ba460a3..9c8ecef3b35 100644
--- a/apollo-common/src/main/java/com/ctrip/framework/apollo/common/entity/BaseEntity.java
+++ b/apollo-common/src/main/java/com/ctrip/framework/apollo/common/entity/BaseEntity.java
@@ -149,6 +149,7 @@ protected ToStringHelper toStringHelper() {
         .add("dataChangeLastModifiedTime", dataChangeLastModifiedTime);
   }
 
+  @Override
   public String toString(){
     return toStringHelper().toString();
   }
diff --git a/apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/component/PortalSettings.java b/apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/component/PortalSettings.java
index 230be5275a6..e8725c50462 100644
--- a/apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/component/PortalSettings.java
+++ b/apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/component/PortalSettings.java
@@ -117,6 +117,7 @@ public HealthCheckTask(ApplicationContext context) {
       }
     }
 
+    @Override
     public void run() {
 
       for (Env env : allEnvs) {
diff --git a/apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/component/RestTemplateFactory.java b/apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/component/RestTemplateFactory.java
index 85611f74452..a99ac98a718 100644
--- a/apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/component/RestTemplateFactory.java
+++ b/apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/component/RestTemplateFactory.java
@@ -47,18 +47,22 @@ public RestTemplateFactory(final HttpMessageConverters httpMessageConverters,
     this.apolloAuditHttpInterceptor = apolloAuditHttpInterceptor;
   }
 
+  @Override
   public RestTemplate getObject() {
     return restTemplate;
   }
 
+  @Override
   public Class<RestTemplate> getObjectType() {
     return RestTemplate.class;
   }
 
+  @Override
   public boolean isSingleton() {
     return true;
   }
 
+  @Override
   public void afterPropertiesSet() throws UnsupportedEncodingException {
 
     PoolingHttpClientConnectionManager connectionManager = new PoolingHttpClientConnectionManager();
diff --git a/apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/controller/SystemInfoController.java b/apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/controller/SystemInfoController.java
index dc30c21c561..a58c26e4359 100644
--- a/apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/controller/SystemInfoController.java
+++ b/apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/controller/SystemInfoController.java
@@ -25,6 +25,7 @@
 import com.ctrip.framework.apollo.portal.environment.Env;
 import com.ctrip.framework.apollo.portal.environment.PortalMetaDomainService;
 import java.util.List;
+import java.util.Objects;
 import javax.annotation.PostConstruct;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -145,6 +146,6 @@ private ServiceDTO[] getServerAddress(String metaServerAddress, String path) {
   }
 
   private boolean isValidVersion(String version) {
-    return !version.equals("java-null");
+    return !Objects.equals(version, "java-null");
   }
 }
diff --git a/apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/entity/po/ServerConfig.java b/apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/entity/po/ServerConfig.java
index 13bf161105d..1e78e29672d 100644
--- a/apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/entity/po/ServerConfig.java
+++ b/apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/entity/po/ServerConfig.java
@@ -74,6 +74,7 @@ public void setComment(String comment) {
     this.comment = comment;
   }
 
+  @Override
   public String toString() {
     return toStringHelper().add("key", key).add("value", value).add("comment", comment).toString();
   }
diff --git a/apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/spi/defaultimpl/DefaultRoleInitializationService.java b/apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/spi/defaultimpl/DefaultRoleInitializationService.java
index 3c18b9dc0bd..b54d20b50ab 100644
--- a/apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/spi/defaultimpl/DefaultRoleInitializationService.java
+++ b/apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/spi/defaultimpl/DefaultRoleInitializationService.java
@@ -57,6 +57,7 @@ public DefaultRoleInitializationService(final RolePermissionService rolePermissi
   }
 
   @Transactional
+  @Override
   public void initAppRoles(App app) {
     String appId = app.getAppId();
 
@@ -91,6 +92,7 @@ public void initAppRoles(App app) {
   }
 
   @Transactional
+  @Override
   public void initNamespaceRoles(String appId, String namespaceName, String operator) {
 
     String modifyNamespaceRoleName = RoleUtils.buildModifyNamespaceRoleName(appId, namespaceName);
@@ -107,6 +109,7 @@ public void initNamespaceRoles(String appId, String namespaceName, String operat
   }
 
   @Transactional
+  @Override
   public void initNamespaceEnvRoles(String appId, String namespaceName, String operator) {
     List<Env> portalEnvs = portalConfig.portalSupportedEnvs();
 
@@ -116,6 +119,7 @@ public void initNamespaceEnvRoles(String appId, String namespaceName, String ope
   }
 
   @Transactional
+  @Override
   public void initNamespaceSpecificEnvRoles(String appId, String namespaceName, String env, String operator) {
     String modifyNamespaceEnvRoleName = RoleUtils.buildModifyNamespaceRoleName(appId, namespaceName, env);
     if (rolePermissionService.findRoleByRoleName(modifyNamespaceEnvRoleName) == null) {
@@ -131,6 +135,7 @@ public void initNamespaceSpecificEnvRoles(String appId, String namespaceName, St
   }
 
   @Transactional
+  @Override
   public void initCreateAppRole() {
     if (rolePermissionService.findRoleByRoleName(SystemRoleManagerService.CREATE_APPLICATION_ROLE_NAME) != null) {
       return;
@@ -158,6 +163,7 @@ public void createManageAppMasterRole(String appId, String operator) {
 
   // fix historical data
   @Transactional
+  @Override
   public void initManageAppMasterRole(String appId, String operator) {
     String manageAppMasterRoleName = RoleUtils.buildAppRoleName(appId, PermissionType.MANAGE_APP_MASTER);
     if (rolePermissionService.findRoleByRoleName(manageAppMasterRoleName) != null) {
diff --git a/apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/spi/defaultimpl/DefaultRolePermissionService.java b/apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/spi/defaultimpl/DefaultRolePermissionService.java
index fc10aacfaa8..dfa057ef36e 100644
--- a/apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/spi/defaultimpl/DefaultRolePermissionService.java
+++ b/apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/spi/defaultimpl/DefaultRolePermissionService.java
@@ -86,6 +86,7 @@ public DefaultRolePermissionService(final RoleRepository roleRepository,
      * Create role with permissions, note that role name should be unique
      */
     @Transactional
+    @Override
     public Role createRoleWithPermissions(Role role, Set<Long> permissionIds) {
         Role current = findRoleByRoleName(role.getRoleName());
         Preconditions.checkState(current == null, "Role %s already exists!", role.getRoleName());
@@ -114,6 +115,7 @@ public Role createRoleWithPermissions(Role role, Set<Long> permissionIds) {
      */
     @Transactional
     @ApolloAuditLog(type = OpType.CREATE, name = "Auth.assignRoleToUsers")
+    @Override
     public Set<String> assignRoleToUsers(String roleName, Set<String> userIds,
                                          String operatorUserId) {
         Role role = findRoleByRoleName(roleName);
@@ -144,6 +146,7 @@ public Set<String> assignRoleToUsers(String roleName, Set<String> userIds,
      */
     @Transactional
     @ApolloAuditLog(type = OpType.DELETE, name = "Auth.removeRoleFromUsers")
+    @Override
     public void removeRoleFromUsers(
         @ApolloAuditLogDataInfluence
         @ApolloAuditLogDataInfluenceTable(tableName = "UserRole")
@@ -169,6 +172,7 @@ public void removeRoleFromUsers(
     /**
      * Query users with role
      */
+    @Override
     public Set<UserInfo> queryUsersWithRole(String roleName) {
         Role role = findRoleByRoleName(roleName);
 
@@ -179,7 +183,7 @@ public Set<UserInfo> queryUsersWithRole(String roleName) {
         List<UserRole> userRoles = userRoleRepository.findByRoleId(role.getId());
         List<UserInfo> userInfos = userService.findByUserIds(userRoles.stream().map(UserRole::getUserId).collect(Collectors.toList()));
 
-        if(userInfos == null){
+        if (CollectionUtils.isEmpty(userInfos)) {
             return Collections.emptySet();
         }
 
@@ -191,6 +195,7 @@ public Set<UserInfo> queryUsersWithRole(String roleName) {
     /**
      * Find role by role name, note that roleName should be unique
      */
+    @Override
     public Role findRoleByRoleName(String roleName) {
         return roleRepository.findTopByRoleName(roleName);
     }
@@ -198,6 +203,7 @@ public Role findRoleByRoleName(String roleName) {
     /**
      * Check whether user has the permission
      */
+    @Override
     public boolean userHasPermission(String userId, String permissionType, String targetId) {
         Permission permission =
                 permissionRepository.findTopByPermissionTypeAndTargetId(permissionType, targetId);
@@ -242,6 +248,7 @@ public List<Role> findUserRoles(String userId) {
         return Lists.newLinkedList(roleRepository.findAllById(roleIds));
     }
 
+    @Override
     public boolean isSuperAdmin(String userId) {
         return portalConfig.superAdmins().contains(userId);
     }
@@ -250,6 +257,7 @@ public boolean isSuperAdmin(String userId) {
      * Create permission, note that permissionType + targetId should be unique
      */
     @Transactional
+    @Override
     public Permission createPermission(Permission permission) {
         String permissionType = permission.getPermissionType();
         String targetId = permission.getTargetId();
@@ -265,6 +273,7 @@ public Permission createPermission(Permission permission) {
      * Create permissions, note that permissionType + targetId should be unique
      */
     @Transactional
+    @Override
     public Set<Permission> createPermissions(Set<Permission> permissions) {
         Multimap<String, String> targetIdPermissionTypes = HashMultimap.create();
         for (Permission permission : permissions) {
diff --git a/apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/spi/defaultimpl/DefaultUserService.java b/apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/spi/defaultimpl/DefaultUserService.java
index 47bcb7a2a18..b5b95374e8b 100644
--- a/apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/spi/defaultimpl/DefaultUserService.java
+++ b/apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/spi/defaultimpl/DefaultUserService.java
@@ -23,12 +23,16 @@
 
 import java.util.Collections;
 import java.util.List;
+import java.util.Objects;
+import org.springframework.util.CollectionUtils;
 
 /**
  * @author Jason Song(song_s@ctrip.com)
  */
 public class DefaultUserService implements UserService {
 
+  private static final String DEFAULT_USER_ID = "apollo";
+
   @Override
   public List<UserInfo> searchUsers(String keyword, int offset, int limit, boolean includeInactiveUsers) {
     return Collections.singletonList(assembleDefaultUser());
@@ -36,7 +40,7 @@ public List<UserInfo> searchUsers(String keyword, int offset, int limit, boolean
 
   @Override
   public UserInfo findByUserId(String userId) {
-    if (userId.equals("apollo")) {
+    if (Objects.equals(userId, DEFAULT_USER_ID)) {
       return assembleDefaultUser();
     }
     return null;
@@ -44,16 +48,20 @@ public UserInfo findByUserId(String userId) {
 
   @Override
   public List<UserInfo> findByUserIds(List<String> userIds) {
-    if (userIds.contains("apollo")) {
+    if (CollectionUtils.isEmpty(userIds)) {
+      return Collections.emptyList();
+    }
+
+    if (userIds.contains(DEFAULT_USER_ID)) {
       return Lists.newArrayList(assembleDefaultUser());
     }
-    return null;
+    return Collections.emptyList();
   }
 
   private UserInfo assembleDefaultUser() {
     UserInfo defaultUser = new UserInfo();
-    defaultUser.setUserId("apollo");
-    defaultUser.setName("apollo");
+    defaultUser.setUserId(DEFAULT_USER_ID);
+    defaultUser.setName(DEFAULT_USER_ID);
     defaultUser.setEmail("apollo@acme.com");
 
     return defaultUser;