Based on your answer, my answer which was listed as incorrect is actually correct.  You asked what was the best way, and the first part of your explanation is that...

2050 may seem a long way away, but does anyone remember the millenium issue?  Assuming that a date at that point is satisfactory is an obvious problem.  It may well...

I avoid nulls wherever possible, preferring a default value.  However, there are situations where NULL is a perfectly valid value in that it means that there is no known value. ...