If you give workspace:FindPartOnRayWithWhitelist() an array with the first index being nil, the function will return anything that the ray hits, including artifacts outside of the whitelist.
The bug happens 100% of the time in studio and on the client.
Here is a quick video demo of the bug happening:
I do not know when the bug started happening.
Notes:
Upon further investigation, if a nil index is present anywhere in the whitelist, the bug will occur.
I’m not sure if everything being considered a descendant of nil is good behaviour, I was just noting that how this currently works is consistent with other APIs. The current behaviour of this function is definitely very unintuitive and should be changed.