Hide a panel if a lookup Dropdown has not been selected (Please select a value...)

Hi All

I have created a form with a cascading dropdown control

I also have 2 panels

I would like to hide these panels until a user selects a value from the first dropdown (Business Unit lookup)

I have added a Calculated Value filed to show the exact value when an item is selected:

If nothing is selected from the dropdown, no value is entered into the Calculated lookup

I have tried various different rules on the panels I want to hide

If I use this formula on a formatting rule, I can hide the correct panel if 'Clients &Industries' is selected:

But what value do I insert into my formula if no item has been selected yet? (and the default value is "Please select a value...")