Laravel Blade速记三元运算符无法正常工作

Question

我正在使用laravel collective来生成我的表单，在其中一个下拉列表中，我有以下三元运算符：

 {!! Form::select('department_id', ['' => 'Please select'] + $departments, isset($user->departmentStaff->department_id) ? $user->departmentStaff->department_id : null , ['class' => 'form-control']) !!}

然而，laravel速记三元运算符不起作用，它会抛出错误：

{!! Form::select('department_id', ['' => 'Please select'] + $departments, $user->departmentStaff->department_id or null , ['class' => 'form-control']) !!}

这来自官方文档：https://laravel.com/docs/5.2/blade#control-structures