bugfix: prefix: [seata.server.raft.ssl] should not be null

[funky-eyes]

• I have registered the PR changes.

Ⅰ. Describe what this PR did

Ⅱ. Does this pull request fix one issue?

fixes #7115

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

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[xingfudeshi]

LGTM

[codecov]

Codecov Report

Attention: Patch coverage is 22.72727% with 34 lines in your changes missing coverage. Please review.

Project coverage is 53.16%. Comparing base (6799dc9) to head (02d6f63).
Report is 2 commits behind head on 2.x.

Files with missing lines	Patch %	Lines
...ies/server/raft/ServerRaftSSLClientProperties.java	25.00%	9 Missing ⚠️
...roperties/server/raft/ServerRaftSSLProperties.java	30.76%	9 Missing ⚠️
...ies/server/raft/ServerRaftSSLServerProperties.java	25.00%	9 Missing ⚠️
...configure/SeataServerEnvironmentPostProcessor.java	0.00%	3 Missing ⚠️
...g/apache/seata/server/cluster/raft/RaftServer.java	0.00%	3 Missing ⚠️
...e/seata/server/instance/ServerInstanceFactory.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x    #7116      +/-   ##
============================================
- Coverage     53.19%   53.16%   -0.04%     
- Complexity     6799     6806       +7     
============================================
  Files          1133     1136       +3     
  Lines         40302    40341      +39     
  Branches       4721     4723       +2     
============================================
+ Hits          21440    21448       +8     
- Misses        16820    16852      +32     
+ Partials       2042     2041       -1     

Files with missing lines	Coverage Δ
...ava/org/apache/seata/common/ConfigurationKeys.java	0.00% <ø> (ø)
...ta/spring/boot/autoconfigure/StarterConstants.java	100.00% <ø> (ø)
...e/properties/server/raft/ServerRaftProperties.java	100.00% <ø> (ø)
...e/seata/server/instance/ServerInstanceFactory.java	58.33% <0.00%> (-2.78%)	⬇️
...configure/SeataServerEnvironmentPostProcessor.java	0.00% <0.00%> (ø)
...g/apache/seata/server/cluster/raft/RaftServer.java	52.45% <0.00%> (ø)
...ies/server/raft/ServerRaftSSLClientProperties.java	25.00% <25.00%> (ø)
...roperties/server/raft/ServerRaftSSLProperties.java	30.76% <30.76%> (ø)
...ies/server/raft/ServerRaftSSLServerProperties.java	25.00% <25.00%> (ø)

... and 5 files with indirect coverage changes