title: override system.assignedto value in a transition
body: <p>I have a rule that in a previous transition sets a default value for the System.AssignedTo. </p>
  
  <p>Now when the state changes, i want to override that value to a different user. </p>
  
  <p>DEFAULT doesn't work, because there is already a value in there. I can't seem to override that value.  Anyone know how that is done?  I've tried empty then default.. but that field is also REQUIRED so empty throws an error.  Regardless that doesn't work either. </p>