[TASK] LinkResult should have return consistent types when serialized to JSON

Right now some properties returns empty string or null when value is empty. i.e. title (null when empty), target ('' string when "empty").

Patch makes all serialized properties behavior consistent (null on empty string values).

Resolves: #95097
Related: #94889
Releases: master
Change-Id: Ib9e6db04bfc165e8dd32bb5092f33f7862696941
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/70881


Tested-by: core-ci <typo3@b13.com>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Tymoteusz Motylewski <t.motylewski@gmail.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Tymoteusz Motylewski <t.motylewski@gmail.com>