Fix potential null-dereference in CommandHandler

[wbzj1110]

resolve #1701

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just added a non-empty judgment

[codecov]

Codecov Report

Merging #1703 (160f9ab) into 5.3.x (ba6e81c) will increase coverage by 0.01%.
The diff coverage is 40.00%.

@@             Coverage Diff              @@
##              5.3.x    #1703      +/-   ##
============================================
+ Coverage     79.71%   79.72%   +0.01%     
- Complexity     5892     5899       +7     
============================================
  Files           423      423              
  Lines         19679    19682       +3     
  Branches       2232     2234       +2     
============================================
+ Hits          15687    15692       +5     
  Misses         2949     2949              
+ Partials       1043     1041       -2     

Impacted Files	Coverage Δ	Complexity Δ
.../java/io/lettuce/core/protocol/CommandHandler.java	76.64% <40.00%> (-0.61%)	103.00 <0.00> (ø)
...io/lettuce/core/masterslave/SentinelConnector.java	65.00% <0.00%> (-17.50%)	6.00% <0.00%> (-2.00%)
...tuce/core/masterslave/SentinelTopologyRefresh.java	84.96% <0.00%> (-1.31%)	35.00% <0.00%> (ø%)
src/main/java/io/lettuce/core/ScanStream.java	86.53% <0.00%> (-1.29%)	24.00% <0.00%> (ø%)
.../io/lettuce/core/dynamic/ReactiveTypeAdapters.java	88.26% <0.00%> (+0.86%)	1.00% <0.00%> (ø%)
...a/io/lettuce/core/protocol/ConnectionWatchdog.java	80.89% <0.00%> (+4.45%)	42.00% <0.00%> (+4.00%)
.../io/lettuce/core/protocol/ReconnectionHandler.java	72.89% <0.00%> (+6.54%)	26.00% <0.00%> (+3.00%)

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[wbzj1110]

I just just added a non-empty judgment ,and I don't know why

codecov/patch — 40.00% of diff hit (target 79.71%)

these happened?(｀・ω・´)