It`s true, my solution of .reduce doesn´t work propertly but when I changed to loop - boolean and be able to represent the null value, it worked perfectly. .)

As I said, your .reduce is not working. JS is weird when it comes to implicit bool -> int conversion, and it's not happenning here.

.reduce works fine, My question is if is something I missed in my solution ..but don´t worries, I´ll figure out!!
Test Passed
There are 500 sheeps in total, not NaN
There are no sheeps at all, you counted NaN

You should return a number, and I'm not sure whether your .reduce is working correctly (and I don't care enough to look into it).

And next time give at least some minimum information concerning your problem except "my code is not working".