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.

• [X] 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:

• [X] My code follows the style guidelines of this project
• [X] My code meets the required code coverage for lines (90% and above)
• [X] My code meets the required code coverage for branches (80% and above)
• [X] 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
• [X] 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 :white_check_mark:

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

Additional details and impacted files

```diff @@ 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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