JENKINS-45198 was fixed in Declarative 1.2 but the env map doesn't seem to populate correctly when using the Kubernetes agent.
 
It looks like the Kubernetes agent is calling `checkout scm` directly instead of the fix Andrew implemented for JENKINS-45198. In the 'checkoutAndRun' method the env variables map is getting populated if anything is returned otherwise it does not populate env.
 
If I skipDefaultCheckout and do the checkout myself it works fine.