Hello Vara, and welcome in this community forum,
Sorry for the delay answering you, it’s indeed a case of False Negative (FN) from implementation of S2755.
Thanks for raising this, and for providing a perfectly self-contained reproducer, this is highly appreciated!
I created the following ticket to handle it, and eventually, fix the rule: SONARJAVA-3212
Finally, please note that latest LTS version of SonarQube is 7.9, and that the fix which will be done for this rule will only be available on the new LTS.
Cheers,
Michael