Fix lettuce NullPointerException (#599)

Author: gzlicanyi

CHANGES.md

@@ -153,6 +153,7 @@ Callable {
 * Support asynchronous invocation in jetty client 9.0 and 9.x plugin
 * Add nacos-client 2.x plugin
 * Staticize the tags for preventing synchronization in JDK 8 
+* Fix NullPointerException in lettuce-5.x-plugin.
 
 #### Documentation
 

apm-sniffer/apm-sdk-plugin/lettuce-5.x-plugin/src/main/java/org/apache/skywalking/apm/plugin/lettuce/v5/RedisChannelWriterInterceptor.java

@@ -101,9 +101,12 @@ private String getArgsKey(RedisCommand<?, ?, ?> redisCommand) {
         CommandArgs<?, ?> args = redisCommand.getArgs();
         if (args == null) {
             return Constants.EMPTY_STRING;
-        } 
+        }
         ByteBuffer firstEncodedKey = args.getFirstEncodedKey();
-        String key = STRING_CODEC.decodeKey(firstEncodedKey);    
+        if (firstEncodedKey == null) {
+            return Constants.EMPTY_STRING;
+        }
+        String key = STRING_CODEC.decodeKey(firstEncodedKey);
         if (StringUtil.isNotEmpty(key) && key.length() > LettucePluginConfig.Plugin.Lettuce.REDIS_PARAMETER_MAX_LENGTH) {
             key = StringUtil.cut(key, LettucePluginConfig.Plugin.Lettuce.REDIS_PARAMETER_MAX_LENGTH) + ABBR;
         }