default values is a special case (and one which I consider to be a bug in python, frankly, since it bites everyone who didn't read up on default arguments before the wrote some code - everyone uses [] as a default argument at some point and then spends an amount of time proportional to the complexity of their program debugging the insane behaviour before noticing. My program was quite long and complex, and I am still bitter.)

I didn't argue, and certainly didn't mean to imply, that it is always better, but in the sort of case we're considering in this example, i.e. we expect a valid time value or None, It really is madness to imply a time value of midnight is "empty".