Jenkins picks a random agent if agent is 'null'

How to reproduce

1. Create a pipeline job with following script 

   pipeline {
       agent none
       stages {
           stage ('This stage should not run anywhere.') {
               agent {
                   label env.NODE_THAT_DOES_NOT_EXIST
               }
               steps {
                   echo "Agent is : " + env.NODE_THAT_DOES_NOT_EXIST
                   echo 'Test'
               }
           }
       }
   }
   

Results

1. The way I expect this to work is if the node does not exist, the Jenkins pipeline should fail saying the "The node does not exist" instead of picking up a random agent from available agents.
2. 

Acceptance criteria

1. Fail the pipeline if the agent is null .