If you want to allow the empty string you can start your regular expression with the 'empty' or operator '|', eg "|^.*foo.*$".
Now the string can be empty or anything with foo in it.

--Hardy

On Wed, 24 Jun 2009 09:47:56 +0200, Alaa Mohsen <alaa.mohsen@egyptdc.com> wrote:

Hello All,
I just realized that PatternValidator checks if the String passed to it
is null or not before checking it's validity, but it doesn't check if the
String is empty. What if someone wants to put a regular expression
constraint on a non mandatory field, and the framework he uses sets this
empty field to an empty string? What do you think?