Yeah, I noticed that, but it comes down to what invarients hold in the code.  Line 48 can be deleted as long as getReachableNT and checkNullability2 isn't called anywhere else.  But of course, code evolves.  Passing as a parameter and avoiding the global is a good way to protect against against that.  My point isn't about line 48 in particular, but rather why the unnecessary use of globals is bad.