I have text box(InvB4Tax) with an expresion of l1cost+l2Cost+L3cost. my problem is that any of those values can be null.
How can i test each value for null. If it is null replace with a numeric zero
<------ this is my expression to calculate value of INVB4Tax
<------ this is my text box that will contain the sum of l1cost+l2cost+l3cost