I'm using a value from an unbound Form Combo Box to limit my Query.

I'm using this expression to limit by City
Like "*" & [Forms]![frm_Search]![cmb_CITY ]& "*"

My Table contains many rows with Null Values for this Field
When I use the above expression the query does not show rows with null
values even when the Form Combo Box value is Null.

I need a query expression that will run only when there is a value in
the Form Combo Box.
If there is a value in the Form Combo Box then limit to that value
If the Form Combo Box is Null do nothing and return all rows