This is an issue with Python as well.

Первая задача которую решил на джаве

If the intention is input validation, this should be specified more clearly.

And isn't that the reason your function should return "INVALID"?

The last description exampe is inconsistent with the specs, which say strictly positive numbers only.

( Haskell )

Example test sumMul 0 0 `shouldBe` Nothing breaks the specs, which says strictly positive numbers only.

If the description lies, please raise an Issue, with the language this happens in, and the exact lie.

8 kyu kata don't need extra tasks.

approved

There should be tests with n=0 and n=1.

Reference solution fails when n is a float with an integer value.

Invalid inputs should be removed from description and sample tests.

This way too tough for 7 kyu I think

The current description is vague and does not clearly outline the conditions for passing.
For an 8kyu the description should be more precise to avoid confusion and for accurate understanding of the requirements.