If you try to declare an empty namespace with `(ns)`, you get an ArityException, but ns-decl? does not test for this.
The attached patch simply tests whether it is at least two items long.
I have previously signed the Clojure CA.
I'm wondering if it's worth updating my patch to also check that the namespace name is a symbol.
I feel like I need some more context here. What is the motivation for making a change in this case? Have you encountered real code in which (ns) causes a problem because tools.namespace accepts it as a valid namespace declaration?