[ISSUE #5996]optimize the RemotingSerializable class code

[hardyfish]

Make sure set the target branch to develop

What is the purpose of the change

close #5996

Brief changelog

optimize the RemotingSerializable class code

Verifying this change

XXXX

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[codecov-commenter]

Codecov Report

Merging #5998 (89ed61d) into develop (b6e0bf3) will decrease coverage by 0.01%.
The diff coverage is 50.00%.

@@              Coverage Diff              @@
##             develop    #5998      +/-   ##
=============================================
- Coverage      43.39%   43.38%   -0.01%     
+ Complexity      8825     8822       -3     
=============================================
  Files           1090     1090              
  Lines          76609    76617       +8     
  Branches       10002    10005       +3     
=============================================
- Hits           33241    33238       -3     
- Misses         39211    39221      +10     
- Partials        4157     4158       +1     

Impacted Files	Coverage Δ
...cketmq/remoting/protocol/RemotingSerializable.java	77.77% <50.00%> (ø)
...apache/rocketmq/broker/longpolling/PopRequest.java	31.03% <0.00%> (-13.80%)	⬇️
...controller/impl/DefaultBrokerHeartbeatManager.java	82.27% <0.00%> (-3.80%)	⬇️
...a/org/apache/rocketmq/filter/util/BloomFilter.java	60.43% <0.00%> (-2.20%)	⬇️
...va/org/apache/rocketmq/store/util/PerfCounter.java	64.39% <0.00%> (-2.10%)	⬇️
...a/org/apache/rocketmq/store/StoreStatsService.java	33.97% <0.00%> (-0.56%)	⬇️
...e/rocketmq/namesrv/routeinfo/RouteInfoManager.java	63.43% <0.00%> (-0.33%)	⬇️
...cketmq/broker/processor/PopBufferMergeService.java	33.41% <0.00%> (-0.24%)	⬇️
...lient/impl/consumer/DefaultMQPushConsumerImpl.java	31.92% <0.00%> (-0.17%)	⬇️
...cketmq/broker/processor/NotificationProcessor.java	10.65% <0.00%> (-0.13%)	⬇️
... and 5 more

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[caigy]

'optimization' is a so generic and fuzzy concept, pls make your description more concrete.

[hardyfish]

'optimization' is a so generic and fuzzy concept, pls make your description more concrete.

toJson does not return an empty object, so just check the null value of the parameter

[hardyfish]

'optimization' is a so generic and fuzzy concept, pls make your description more concrete.

so my change is to remove toJson's null check and just check the null value of the parameter.

[mxsm]

LGTM~

[hardyfish]

please help merge.