How to check for elements that are undefined in custom rulesets

[rkInfo9]

I have a yaml file I am trying to lint. Why doesn't the truthy function see that element is missing. I tried the function "undefined" too. When I lint, I am not seeing any errors. How do I check for custom elements that are undefined? Any help would be appreciated.

Example Spec: (only a part of it)

openapi: 3.0.0
info:
  title: BillingMs
  description: This micro service involves retrieval of billing details
  my-custom-element:   
      teamName: Billing
      #teamEmail: [email protected] 

Ruleset:

my-custom-rule:
   description: "Team Email Rule" 
   given: "$.info.my-custom-element.teamEmail"
   severity: warn
   then:
      - function: truthy