[ic] strange database update behavior

[DB]

I just noticed a strange (at least to me) behavior in a form that I've
been using to update a mysql database table.

The update of a text-type column fails if I attempt to submit an empty
entry. I see no error in the IC logs. If I instead submit a single space
(or any other non-empty string) then the update works.

The column definition is

Database  transactions  COLUMN_DEF   "notes=text"

Can anyone explain?

DB