public HR(ILeaveRequestHandler nextHandler) : base(nextHandler)
 {
 }
 public Supervisor(ILeaveRequestHandler nextHandler) : base(nextHandler)
 {
 }
 public ProjectManager(ILeaveRequestHandler nextHandler) : base(nextHandler)
 {
 }
 public ILeaveRequestHandler(ILeaveRequestHandler nextHandler)
 {
     this.nextHandler = nextHandler;
 }