bugfix: jdbc parameter set null

[jsbxyyx]

Ⅰ. Describe what this PR did

jdbc parameter set null, cause error.

Ⅱ. Does this pull request fix one issue?

fixes #1852

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

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[codecov-io]

Codecov Report

Merging #1879 into develop will decrease coverage by 0.14%.
The diff coverage is 50%.

@@              Coverage Diff              @@
##             develop    #1879      +/-   ##
=============================================
- Coverage      55.36%   55.22%   -0.15%     
+ Complexity      2379     2376       -3     
=============================================
  Files            422      422              
  Lines          14331    14305      -26     
  Branches        1717     1679      -38     
=============================================
- Hits            7935     7900      -35     
+ Misses          5656     5649       -7     
- Partials         740      756      +16

Impacted Files	Coverage Δ	Complexity Δ
...a/rm/datasource/sql/druid/BaseMySQLRecognizer.java	94.44% <50%> (-2.7%)	12 <0> (ø)
...asource/sql/druid/oracle/BaseOracleRecognizer.java	94.44% <50%> (-2.7%)	12 <0> (ø)
...obuf/convertor/BranchRegisterRequestConvertor.java	88% <0%> (-8%)	3% <0%> (ø)
...buf/convertor/GlobalLockQueryRequestConvertor.java	92.59% <0%> (-7.41%)	3% <0%> (ø)
...otobuf/convertor/GlobalStatusRequestConvertor.java	94.73% <0%> (-5.27%)	3% <0%> (ø)
...obuf/convertor/GlobalRollbackRequestConvertor.java	94.73% <0%> (-5.27%)	3% <0%> (ø)
...otobuf/convertor/GlobalCommitRequestConvertor.java	94.73% <0%> (-5.27%)	3% <0%> (ø)
...protobuf/convertor/RegisterTMRequestConvertor.java	95.45% <0%> (-4.55%)	3% <0%> (ø)
...protobuf/convertor/RegisterRMRequestConvertor.java	91.66% <0%> (-4.17%)	3% <0%> (ø)
...otobuf/convertor/BranchReportRequestConvertor.java	92.59% <0%> (-3.71%)	3% <0%> (ø)
... and 20 more

[zjinlei]

LGTM

[slievrly]

LGTM