This has already been fixed in the current development tree.
> Here is a patch against 7.0.2 that fixes the bug where casting a NULL
> returned from a select to type date fails with the error:
> Unable to convert null timestamp to date
>
[ Attachment, skipping... ]
--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026