[ISSUE #9943] Remove redundant containsKey check in checkBrokerConfig (#9944)

Author: yx9o

client/src/main/java/org/apache/rocketmq/client/Validators.java

@@ -131,11 +131,10 @@ public static void checkTopicConfig(final TopicConfig topicConfig) throws MQClie
     }
 
     public static void checkBrokerConfig(final Properties brokerConfig) throws MQClientException {
-        // TODO: use MixAll.isPropertyValid() when jdk upgrade to 1.8
-        if (brokerConfig.containsKey("brokerPermission")
-            && !PermName.isValid(brokerConfig.getProperty("brokerPermission"))) {
+        String brokerPermission = brokerConfig.getProperty("brokerPermission");
+        if (brokerPermission != null && !PermName.isValid(brokerPermission)) {
             throw new MQClientException(ResponseCode.NO_PERMISSION,
-                String.format("brokerPermission value: %s is invalid.", brokerConfig.getProperty("brokerPermission")));
+                    String.format("brokerPermission value: %s is invalid.", brokerPermission));
         }
     }
 }