fix: Incorrect conversion to string when equals to null

[o-kopysov]

Pull Request

Description

Current PR contains a bug fix for the incorrect conversion to string when the queue element equals null.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Code cleanup/refactoring
• Documentation update
• This change requires a documentation update
• CI system update
• Test Coverage update

Testing

Checked by functional tests.

Checklist:

• My code follows the style guidelines of this project
• My code meets the required code coverage for lines (90% and above)
• My code meets the required code coverage for branches (80% and above)
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.88%. Comparing base (9f5d6ba) to head (3016cfe).

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #619      +/-   ##
============================================
+ Coverage     93.46%   93.88%   +0.42%     
  Complexity      623      623              
============================================
  Files            52       52              
  Lines          2127     2127              
  Branches        247      247              
============================================
+ Hits           1988     1997       +9     
+ Misses           65       56       -9     
  Partials         74       74              

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[o-konoval]

LGTM