Use basic type

[koppor]

Tries to avoid boxing and unboxing in BibEntryWriter

Mandatory checks

• I own the copyright of the code submitted and I license it under the MIT license
• [/] Change in CHANGELOG.md described in a way that is understandable for the average user (if change is visible to the user)
• [/] Tests created for changes (if applicable)
• [/] Manually tested changed features in running JabRef (always required)
• [/] Screenshots added in PR description (if change is visible to the user)
• [/] Checked developer's documentation: Is the information available and up to date? If not, I outlined it in this pull request.
• [/] Checked documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request to the documentation repository.

[trag-bot]

The method signature change from Boolean to boolean is correct, but the pull request title should contain a short title of the issue fixed or what the PR addresses, not just 'Fix issue xyz'.

[github-actions]

The build for this PR is no longer available. Please visit https://builds.jabref.org/main/ for the latest build.