Process model.. variable.. didn't get the values

I had created a process model to add employees, leave request, and leave approval.

in leave approval, it doesn't get the employee id by itself. I had configured everything.

it is showing an error in the expression rule... that the value should not be null... the value is not null at the table... I had checked with the expression rule... it gives the data by entering the id... 

but here its showing error.