nullInputStream is not a class, it's a method in the System class.
Joined: Oct 30, 2001
And, looking at the source of the System class, they're very strange methods, too. See the comment above them: -
I don't think there's much to be gained by looking into the detail of these methods. They just look like some nasty hack needed for the special requirements of initialisation of this internal Java implementation class.
If you're looking for a PrintStream that writes to a null device, these System methods do not do that. You're better off looking at one of the examples you already found on the Web.