Divergence of a vector field

Hello,

I am new to COMSOL and I am trying to build a physics interface module. I would like to calculate the divergence of current density. I defined a variable for the same, but when I input the divergence of current density in the variable declaration, an error pops up saying "Expression of the nable operator is not supported".

Can anyone tell me why I see this error.? How else I can calculate the divergence?

Thanks,
Aravinth.