So I re-read the specs. I am trying to wrap my brain around why this package would exist.
- According to graphql specs, a query should trigger an error if a null value exists on a field with !. We know dgraph does not do this, as we use @cascade to get around it. This is a separate issue, but needs to be looked at.
- We know it does, however, throw an error when passing an argument to a variable with !, which works as expected.
So it seems the package exists to throw an error specifically when using add / update mutations, which is what we want. So, you are right. 
Like I said before, this still could be fixed with the right @auth directive (once you guys look at the field validation needs you can solve with very little coding by adding update-after).
We need to be able to implement the @nonNull directive in Dgraph Cloud, which would be on the Dgraph Team to do.
I am pro doing this.
J