macaddr data type issue

Hi,

I am looking for some confirmation and perhaps some explanation of and for
the following observation.  If I use "000000-000000" as input to a
macaddr data type element in my database no value appears to be stored.  I
was intending to use this value as a "missing data" marker in my
application.  I've looked for documentation high and low but haven't been
able to find anything regarding this behavior.  I did stumble upon some
source code, which I believe is relevant, which suggests that the code's
author was planning for a "missing value's" value.  Unfortunately, the
macaddr data type output function does not seem to produce the
"00:00:00:00:00:00" string that I would expect.

It seems to me that if I were to input and the database would accept
"000000-000000" as indicative of missing values that the database should
output such a value when it is encountered in a dataset.  At very least,
it would seem that some additional documentation might be warranted. I
suspect I am missing something here.  Can anyone offer confirmation of
this behavior and an explanation for, what seems to me to be, this
counter-intuitive behavior?

Thanks for your time and effort on my behalf.

Gayland