Made the AccountTest::testNullArguments() test more explicit

[dexterlohnes]

Hi all.

I was reading over the tests in order to get a better idea of where to start, and while this test was written in as few lines of code as possible, for a newcomer to the project(s) like me it pays off to have things be a little more explicit when reading tests as a form of documentation in and of themselves.

As such, I've provided some minor changes to a single test in order to better reveal its intent to someone like me who isn't yet familiar with the codebase.