[type:refactor][ISSUE #5344] Standardized null detection coding

[MRgenial]

Standardized null detection coding in shenyu-admin

Make sure that:

• You have read the contribution guidelines.
• You submit test cases (unit or integration tests) that back your changes.
• Your local test passed ./mvnw clean install -Dmaven.javadoc.skip=true.

[MRgenial]

May I ask where this CI build error was caused? I have not made any modifications to anything here. @yu199195

[codecov-commenter]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (9a29e10) 61.96% compared to head (52eca3f) 61.95%.

Files	Patch %	Lines
...u/admin/service/impl/AlertDispatchServiceImpl.java	0.00%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5345      +/-   ##
============================================
- Coverage     61.96%   61.95%   -0.02%     
- Complexity     8720     8721       +1     
============================================
  Files          1255     1255              
  Lines         38356    38356              
  Branches       3675     3675              
============================================
- Hits          23766    23762       -4     
- Misses        12480    12484       +4     
  Partials       2110     2110              

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