diff --git a/apollo-client/src/main/java/com/ctrip/framework/apollo/internals/RemoteConfigRepository.java b/apollo-client/src/main/java/com/ctrip/framework/apollo/internals/RemoteConfigRepository.java
index 58984015..155f4c58 100644
--- a/apollo-client/src/main/java/com/ctrip/framework/apollo/internals/RemoteConfigRepository.java
+++ b/apollo-client/src/main/java/com/ctrip/framework/apollo/internals/RemoteConfigRepository.java
@@ -260,7 +260,7 @@ private ApolloConfig loadApolloConfig() {
 
             ConfigSyncType configSyncType=ConfigSyncType.fromString(result.getConfigSyncType());
 
-            if (configSyncType == ConfigSyncType.INCREMENTALSYNC) {
+            if (configSyncType == ConfigSyncType.INCREMENTAL_SYNC) {
 
               ApolloConfig previousConfig = m_configCache.get();
 
diff --git a/apollo-client/src/test/java/com/ctrip/framework/apollo/internals/RemoteConfigRepositoryTest.java b/apollo-client/src/test/java/com/ctrip/framework/apollo/internals/RemoteConfigRepositoryTest.java
index e0334ccb..e5e44920 100644
--- a/apollo-client/src/test/java/com/ctrip/framework/apollo/internals/RemoteConfigRepositoryTest.java
+++ b/apollo-client/src/test/java/com/ctrip/framework/apollo/internals/RemoteConfigRepositoryTest.java
@@ -33,7 +33,6 @@
 import com.ctrip.framework.apollo.build.MockInjector;
 import com.ctrip.framework.apollo.core.dto.*;
 import com.ctrip.framework.apollo.core.enums.ConfigSyncType;
-import com.ctrip.framework.apollo.core.enums.ConfigurationChangeType;
 import com.ctrip.framework.apollo.core.signature.Signature;
 import com.ctrip.framework.apollo.enums.ConfigSourceType;
 import com.ctrip.framework.apollo.exceptions.ApolloConfigException;
@@ -487,7 +486,7 @@ private ApolloConfig assembleApolloConfigWithIncrementalSync(List<ConfigurationC
     ApolloConfig apolloConfig =
             new ApolloConfig(someAppId, someClusterName, someNamespace, someReleaseKey);
 
-    apolloConfig.setConfigSyncType(ConfigSyncType.INCREMENTALSYNC.getValue());
+    apolloConfig.setConfigSyncType(ConfigSyncType.INCREMENTAL_SYNC.getValue());
     apolloConfig.setConfigurationChanges(configurationChanges);
     return apolloConfig;
   }
diff --git a/apollo-core/src/main/java/com/ctrip/framework/apollo/core/dto/ConfigurationChange.java b/apollo-core/src/main/java/com/ctrip/framework/apollo/core/dto/ConfigurationChange.java
index e4595a59..7296dc4b 100644
--- a/apollo-core/src/main/java/com/ctrip/framework/apollo/core/dto/ConfigurationChange.java
+++ b/apollo-core/src/main/java/com/ctrip/framework/apollo/core/dto/ConfigurationChange.java
@@ -17,7 +17,6 @@
 package com.ctrip.framework.apollo.core.dto;
 
 
-import com.ctrip.framework.apollo.core.enums.ConfigurationChangeType;
 
 /**
  * Holds the information for a Configuration change.
diff --git a/apollo-core/src/main/java/com/ctrip/framework/apollo/core/enums/ConfigSyncType.java b/apollo-core/src/main/java/com/ctrip/framework/apollo/core/enums/ConfigSyncType.java
index 48881558..540c2d9a 100644
--- a/apollo-core/src/main/java/com/ctrip/framework/apollo/core/enums/ConfigSyncType.java
+++ b/apollo-core/src/main/java/com/ctrip/framework/apollo/core/enums/ConfigSyncType.java
@@ -18,15 +18,13 @@
 
 import com.ctrip.framework.apollo.core.utils.StringUtils;
 
-import java.util.stream.Stream;
-
 /**
  * This enum represents all the possible Configuration sync  from apollo-config
  *
  * @author jason
  */
 public enum ConfigSyncType {
-  FULLSYNC("FullSync"), INCREMENTALSYNC("IncrementalSync");
+  FULL_SYNC("FullSync"), INCREMENTAL_SYNC("IncrementalSync"), UNKNOWN("UnKnown");
 
   private final String value;
 
@@ -46,14 +44,14 @@ public enum ConfigSyncType {
    */
   public static ConfigSyncType fromString(String value) {
     if (StringUtils.isEmpty(value)) {
-         return FULLSYNC;
+      return FULL_SYNC;
     }
     for (ConfigSyncType type : values()) {
             if (type.value.equals(value)) {
                 return type;
              }
          }
-       throw new IllegalArgumentException("Invalid ConfigSyncType: " + value);
+    return UNKNOWN;
 
   }
 
diff --git a/pom.xml b/pom.xml
index f1061ce2..a255aabd 100644
--- a/pom.xml
+++ b/pom.xml
@@ -60,7 +60,7 @@
   </developers>
 
   <properties>
-    <revision>2.5.0-SNAPSHOT</revision>
+    <revision>2.4.0-SNAPSHOT</revision>
     <java.version>1.8</java.version>
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     <spring-boot.version>2.7.18</spring-boot.version>