fix NPE when ReleaseComment is null.

[Accelerator96]

fix ReleaseComment NullPointerException。

[codecov-io]

Codecov Report

Merging #2814 into master will decrease coverage by 0.06%.
The diff coverage is 0%.

@@             Coverage Diff              @@
##             master    #2814      +/-   ##
============================================
- Coverage     50.48%   50.41%   -0.07%     
+ Complexity     2085     2083       -2     
============================================
  Files           414      414              
  Lines         12668    12668              
  Branches       1294     1295       +1     
============================================
- Hits           6395     6387       -8     
- Misses         5820     5827       +7     
- Partials        453      454       +1

Impacted Files	Coverage Δ	Complexity Δ
...ponent/emailbuilder/ConfigPublishEmailBuilder.java	1.83% <0%> (ø)	1 <0> (ø)	⬇️
...work/apollo/biz/message/DatabaseMessageSender.java	56.25% <0%> (-10.42%)	6% <0%> (-2%)
...mework/apollo/portal/component/PortalSettings.java	65.07% <0%> (-4.77%)	5% <0%> (ø)

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[coveralls]

Coverage decreased (-0.06%) to 54.002% when pulling 22d39f5 on Accelerater:#2801 into 5c5deb7 on ctripcorp:master.

[nobodyiam]

LGTM