Self-Checking Math Input for Undefined Values

I am using the following CL code to allow students to self-check contents of a table (example)

cellContent(1,3): when table7.cellContent(1,2)= “”
when table7.cellNumericValue(1,2)=7.2
otherwise “:x:

This works for finite answers, and when I enter in a range of values (for repeating decimals). The issue I am running into is if, for example, the correct answer is “1/0”, which is undefined. Does anyone know how I would write “undefined” in the validation statement?

This would check if a cell has a fraction with a denominator of 0.

p = patterns
zeroDen = p.fraction(p.number,p.number.satisfies(`x=0`) )
check11 = zeroDen.matches(this.cellContent(1,1))