style: resolve IMC_IMMATURE_CLASS_COLLECTION_RETURN

[vil02]

This PR fixes the failing CI in #6254.

#6254 updates the fb-contrib (spotbugs plugin) and introduces lint IMC_IMMATURE_CLASS_COLLECTION_RETURN.

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized it.
• All filenames are in PascalCase.
• All functions and variable names follow Java naming conventions.
• All new algorithms have a URL in their comments that points to Wikipedia or other similar explanations.
• All new code is formatted with clang-format -i --style=file path/to/your/file.java

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.98%. Comparing base (3b9bdcc) to head (aecf9e8).
⚠️ Report is 430 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #6256   +/-   ##
=========================================
  Coverage     73.98%   73.98%           
+ Complexity     5345     5344    -1     
=========================================
  Files           677      677           
  Lines         18652    18652           
  Branches       3621     3621           
=========================================
  Hits          13799    13799           
  Misses         4294     4294           
  Partials        559      559           

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