Regular expression for required iba value

Hello,

I'm trying to make a attribute dependent of the value of another attribute.

Both are IBA's.

So we have an attribute "number of bends" this is filled in automatic with a string number.

The second attribute "overrule qty" should be required if the other one is greater than 0.

So I tried to do it like this:

But this doesn't seem to work, my guess is that number of bends is defined as a string and not as an integer, but this we can't change that easily.

Does somebody know a trick to do this, or another way to get my goal?

Thanks in advance