Max() function in weak form

1

Hello,

I want to include a term in the weak formulation which is a max() function like this

max(0,u)

where u is the unknown of the problem. If I just include this term in the weak form I get the following error:
UFL conditions cannot be evaluated as bool in a Python context.

How can I implement this?

Thank you

2 
import ufl
ufl.Max