Support question

with the newest version 0.12.15 I got the following error: Unreachable statement - code above always terminates.
Here is some code which reproduces this error: https://phpstan.org/r/d172d90f-95d0-4fdb-9a4b-74e6a0e2a9f9 (extracted from this file: https://github.com/shopware/platform/blob/6.1/src/Core/Framework/Api/Serializer/JsonApiDecoder.php)

I don't understand what the problem is here 🙈 maybe you guys could help me out