You see, I actually don't know an inkling of Haskell so I just assumed that since the provided solution and test cases passed, it would work. There are some random tests involved, maybe those give negative inputs. How would I fix that?

Approved!

Sorry, just saw this now. Can't find it, can you link it in a comment?

Well yes it makes LOGICAL sense, this is a program. We should be told what to do, especially since we're told how to handle even numbers. How hard can it be to add more detail into a description?

C++ translation Kumited!

Error reporting is still a bit wonky, but that's beyond my scope

Now just hold those test cases right there, the third basic test case (in Java at least) is flatly incorrect. After the two examples before it PROVE that 101 and 107 are both prime, the answer to the third should be {101, 107}, no? So why does it want null as an answer?

This happens three times throughout the basic tests, and my code has a manual workaround for each of them to give the answer you want. My code always passed all the random tests, so it SHOULD be correct.

Approved!

Still cannot be merged.

I almost approved it, but got an error message. I modified the description a bit and added C++, so maybe you need to update your translation?

Nice! Just a few minor things: the error reporting on a failed test case, it's... not there. Also in your description, you have "...the returned String has no leading of trailing spaces." :D