default list of files from () to None, and explicitly test for None
before defaulting to sys.argv[1:].  This means that if you pass in an
explicit empty list, it will read stdin instead of defaulting to
sys.argv[1:].  This fixes a buglet in the test script (when called
with options but without files, it chokes when it tries to interpret
the options as files).

Lawrence adds: "I suspect that this is a safe change, because I can't
imagine someone actively passing in an empty list when they want
sys.argv used."

I agree.