Use console.log() to print your answer before returning

When an array in the array is null or empty, the method should return 0 too!

You're trying to read the length of null, that's what the error says. You have to check if it is an array first.

In JavaScript I just floored seconds and it worked without any rounding. Had frustrated experience because of this "round it to nearest second".
After reading issues section I confirmed what I suspected, author derped a bit here and refused to accept that.
Some of the tests are mathematically incorrect.
Edit: NVM, rounding down is not rounding, it is flooring.