bugfix: protostuff undo log get default content

[iapplejohn]

Ⅰ. Describe what this PR did

Return a byte array with one element so that the program would not throw javax.sql.rowset.serial.SerialException.

Ⅱ. Does this pull request fix one issue?

fixes #1848

Ⅲ. Why don't you add test cases (unit test/integration test)?

MySQLUndoLogManagerTest.testInsertUndoLog could not showcase the issue, for it uses mock driver.

Ⅳ. Describe how to verify it

Utilize MySQL server

Ⅴ. Special notes for reviews

[jsbxyyx]

LGTM

[slievrly]

add UT for decode(getDefaultContent())

[codecov-io]

Codecov Report

Merging #1856 into develop will increase coverage by 0.06%.
The diff coverage is 100%.

@@              Coverage Diff              @@
##             develop    #1856      +/-   ##
=============================================
+ Coverage      55.05%   55.12%   +0.06%     
- Complexity      2355     2359       +4     
=============================================
  Files            422      422              
  Lines          14279    14281       +2     
  Branches        1712     1712              
=============================================
+ Hits            7861     7872      +11     
+ Misses          5688     5681       -7     
+ Partials         730      728       -2

Impacted Files	Coverage Δ	Complexity Δ
...m/datasource/undo/parser/JacksonUndoLogParser.java	71.25% <100%> (+0.73%)	7 <2> (+1)	⬆️
...atasource/undo/parser/ProtostuffUndoLogParser.java	44.89% <100%> (+2.04%)	5 <1> (+1)	⬆️
...server/store/file/FileTransactionStoreManager.java	60.19% <0%> (+1.31%)	29% <0%> (ø)	⬇️
.../datasource/undo/parser/FastjsonUndoLogParser.java	85.71% <0%> (+14.28%)	4% <0%> (+1%)	⬆️
...a/rm/datasource/undo/parser/KryoUndoLogParser.java	90.9% <0%> (+27.27%)	4% <0%> (+1%)	⬆️

[jsbxyyx]

@iapplejohn please relation user.email to github email, user.name to github account.

[iapplejohn]

@jsbxyyx , Shall I delete the previous commits and re-submit with the github username and email?

[jsbxyyx]

@iapplejohn git commit --amend update last commit.

[slievrly]

LGTM

[xingfudeshi]

LGTM.

[zjinlei]

retry ci