previous property
      
      State?
      get
      previous
      
    
    
    
Implementation
State? get previous {
  return _previous;
}
      
      set
      previous
      (State? previous) 
      
    
    
    
Implementation
set previous(State? previous) {
  if (_previous == null && previous != null) {
    _previous = previous;
    return;
  }
  throw StateError("Unable to set 'previous'");
}