Hey, I had issues with that case at first as well, but remember the structure of the variables does not depend on any strings or integers within them. i.e ['[','s'] has the same structure as [1,2] if I am not mistaken. So the data types within the list actually do not matter, what does matter is the structure, i.e [] of the list. That case is used to invalidate string conversions of the entire list.

Some well done List comprehension. Extremelly clever solution

Great initiation Kata