Ryan, I have reviewed the documentation at https://docs.python.org/3/library/argparse.html#nargs and must admit that there is not a definitive answer that I can see regarding the defined behavior should there be no command line arguments that are in fact remaining. One could certainly argue that the empty list is the expression of the fact that no remaining arguments could be found. One can also argue that when seeking the remaining arguments, a list that may be zero to many elements in size, that by definition there cannot be a default.

Can you cite any documentation that would support your claim?