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