NULL vs. Empty String

Hi All,

Apologies for cross-posting.

I've ported a mod_perl application from Oracle to PosgreSQL, but have run
into a difference that's significant for web work. When I get a form field
submitted, if it's empty, mod_perl assumes it to be an empty string ('').
When I inserted empty strings into Oracle tables, Oracle assumed they were
NULL and inserted them as such. Postgres, OTOH, seems to insert it as an
empty string instead. While I realize that the Posgres interpretation is
perhaps the more precise of the two, it was a feature of Oracle that I
rather liked.

Is there a way to get Posgres to assume that a '' insert should be a NULL
insert? And if not, does anyone know of a way to get mod_perl to make that
assumption instead?

TIA,

David