But man, could you take a look at this Kata, I trully beleive there must be a error related to the test: "ShouldWorkForWhitespace", because its expecting to return a empty string of size 4, it doesnt make sense.

The issue tag is for tracking problems with a kata that need to be addressed. You're asking about your own code, please don't use use issue for that. Use question or no tag at all.

For debugging your solution, https://docs.codewars.com/training/troubleshooting might be useful.

I keep having this error, and I dont know why, it doensnt make sense... Its C#, this is the test I can't
to get to work.

Test Failed
Whitespace should work too!
Expected string length 4 but was 0. Strings differ at index 0.
Expected: " "
But was: <string.Empty>
-----------^

how come, I didnt even know this method existed.