regular expression - 4 digits only OR null
 

Hi guys,

I had set a post code field as not mandatory, 4 characters, user editable etc, but when a used goes in and sets it to a null value it errors because the regular expression I used was:

[0-9]

what would I put in the reg exp field that would permit either a null entry OR 4 numerals?

At the moment I have removed the reg exp altogether but that then causes other issues with a script that is expecting 4 digit postcodes as input.

I can't see the way using the guide from prec help;

Best regards,
Will