Fixed

The default tests are not here to give you the solution, by the way, the null case is explicitly quoted in the subject description.

It takes far too long if you copy/paste each data one by one instead of using a simple regex replace in your favorite text-editor.

The abstract inheritance is here to make sure everyone understood the principle of inheritance.

Kata are supposed to give challenges of many kinds. Here the challenges (depending on your Java level) are mostly within the algorithm and technical knowledge of the library/language.

If the Kata is bugged in some way, you can mark it as "Major Issue" but I doubt the arguments you just said are enough consideration.
If you want a higher level Kata well this one is only 6kyu, you should take a look elsewhere.