Fix for issue 8396: filter out the empty field

[tomlinn]

Fixes #8396

Only show deprecated fields tab if they contain values

Descripion

Fixes #8396 by filtering out the empty deprecated fields.
The issue was caused because it always returns a valid deprecated field set but didn't check whether is empty or not.

JabRef version

5.4 (latest release)

Operating system

Mac OS

Details on version and operating system

Monterey 12.2.1

Before

After

PR Checklist

• Change in CHANGELOG.md described in a way that is understandable for the average user (if applicable)
• Tests created for changes (if applicable)
• Manually tested changed features in running JabRef (always required)
• Screenshots added in PR description (for UI changes)
• 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.

[Siedlerchr]

Please check the codestyle, see here for how to impot the style https://github.com/JabRef/jabref/tree/main/config

[Siedlerchr]

I was so free to replace your solution with a more simple one liner to get that PR in asap.

[mlep]

@tomlinn Thank you for fixing this issue, hence making JabRef a better software! If you are looking for another issue to solve, this one is related to the Deprecated fields: #7757