fix: replace spring stringUtils to netty stringUtil, and add comment

Signed-off-by: xujie <mikawudi@qq.com>

redisson/src/main/java/org/redisson/config/SentinelServersConfig.java

@@ -197,6 +197,14 @@ public class SentinelServersConfig extends BaseMasterSlaveServersConfig<Sentinel
         return checkSlaveStatusWithSyncing;
     }
 
+    /**
+     * check node status from sentinel with 'master-link-status' flag
+     * <p>
+     * Default is <code>true</code>
+     *
+     * @param checkSlaveStatusWithSyncing - boolean value
+     * @return config
+     */
     public SentinelServersConfig setCheckSlaveStatusWithSyncing(boolean checkSlaveStatusWithSyncing) {
         this.checkSlaveStatusWithSyncing = checkSlaveStatusWithSyncing;
         return this;

redisson/src/main/java/org/redisson/connection/SentinelConnectionManager.java

@@ -20,6 +20,7 @@ import io.netty.util.NetUtil;
 import io.netty.util.concurrent.Future;
 import io.netty.util.concurrent.FutureListener;
 import io.netty.util.concurrent.ScheduledFuture;
+import io.netty.util.internal.StringUtil;
 import org.redisson.api.NatMapper;
 import org.redisson.api.NodeType;
 import org.redisson.api.RFuture;
@@ -34,7 +35,6 @@ import org.redisson.misc.RedisURI;
 import org.redisson.misc.RedissonPromise;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
-import org.springframework.util.StringUtils;
 
 import java.net.InetSocketAddress;
 import java.util.*;
@@ -599,7 +599,7 @@ public class SentinelConnectionManager extends MasterSlaveConnectionManager {
 
     private boolean isSlaveDown(String flags, String masterLinkStatus) {
         boolean baseStatus = flags.contains("s_down") || flags.contains("disconnected");
-        if (this.checkSlaveStatusWithSyncing && StringUtils.hasText(masterLinkStatus)) {
+        if (this.checkSlaveStatusWithSyncing && !StringUtil.isNullOrEmpty(masterLinkStatus)) {
             return baseStatus || masterLinkStatus.contains("err");
         }
         return baseStatus;