fix baggage contains null

[OrezzerO]

Motivation:

If baggage contains null value, putAll method of. ConcurrentHashMap will throw NPE.

[codecov]

Codecov Report

Merging #1140 (e425e01) into master (303ae5e) will decrease coverage by 0.07%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master    #1140      +/-   ##
============================================
- Coverage     71.07%   71.00%   -0.08%     
+ Complexity      833      831       -2     
============================================
  Files           405      405              
  Lines         17100    17108       +8     
  Branches       2669     2670       +1     
============================================
- Hits          12154    12147       -7     
- Misses         3561     3582      +21     
+ Partials       1385     1379       -6     

Impacted Files	Coverage Δ
.../com/alipay/sofa/rpc/context/RpcInvokeContext.java	81.48% <100.00%> (+0.48%)	⬆️
...fa/rpc/transport/http/SyncInvokeClientHandler.java	51.85% <0.00%> (-33.34%)	⬇️
.../rpc/transport/http/Http2ClientChannelHandler.java	60.52% <0.00%> (-15.79%)	⬇️
...ipay/sofa/rpc/message/http/HttpResponseFuture.java	46.66% <0.00%> (-4.45%)	⬇️
.../main/java/com/alipay/sofa/rpc/event/EventBus.java	80.39% <0.00%> (-3.93%)	⬇️
...c/transport/http/AbstractHttp2ClientTransport.java	76.64% <0.00%> (-2.40%)	⬇️
...ay/sofa/rpc/client/AllConnectConnectionHolder.java	60.76% <0.00%> (+1.02%)	⬆️
...pay/sofa/rpc/transport/ClientTransportFactory.java	78.46% <0.00%> (+1.53%)	⬆️
.../alipay/sofa/rpc/metrics/lookout/RpcLookoutId.java	90.47% <0.00%> (+1.58%)	⬆️
... and 2 more

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[chuailiwu]

LGTM

[EvenLjj]

LGTM