JT-19867: Setting String field in Workflow results in value "jetbrains.youtrack.workflow.wrappers.MutableIterableWrapper@1317b85"

What steps will reproduce the problem?
1. Create Bill As field as type String
2. Create the following workflow

rule Set BillAs value to Support or Feature when Time-Track as Support is updated 
 
when Time-Track as Support != null && (Time-Track as Support.changed || Release versions.changed) { 
  var billAs = Release versions + "::Feature"; 
  if (Time-Track as Support == {Yes}) { 
    billAs = Release versions + "::Support"; 
  } 
   
  Bill As = billAs; 
}

3. Create a new Issue or change value of Time-Track as Support field

What is the expected result?
Would expect the value of Bill As field to be Relase Version::Feature

What happens instead?
Bill As field gets set to jetbrains.youtrack.workflow.wrappers.MutableIterableWrapper@1317b85::Feature

Screenshot attached