How to uncheck checkboxes when a is empty - or how to not calculate non values

I have 2 numeric fields. When one field is greater than or equal to the second field a checkbox is checked. When the field is empty, what code do you use to ensure the checkbox is unchecked???

So far I'm using the following if statement using FormCalc and the calculation drop-down:

if (NumericField14 >= NumericField15) then

  this.rawValue = 1;

else

  this.rawValue = 0;

  endif

So by default it looks like this:

How do you get the statement to not count non-values or nulls?? I've tried adding the following null statement in but I get an error message:

(theField.isNull | theField == "")

Any help is appreciated!