试图在Laravel工厂中种植Faker会产生PHP错误＆＃39; Undefined offset＆＃39;

Question

我在Laravel 5.5中有以下工厂

use Faker\Generator as Faker;

$factory->define(App\Student::class, function (Faker $faker, $form) {
    //$faker->addProvider(new \Faker\Provider\SIMS($faker));
    $faker->seed(1234);
    echo $faker->name;
});

当我运行php artisan db:seed时，我得到的错误In Base.php line 194: Undefined offset: -57的偏移量会有所不同，具体取决于我用于$faker->seed(1234)的值。让这条线离开工厂会导致种子成功运行，但显然我每次都会得到不同的数据，因此需要为Faker种下。

Base.php是Faker的一部分，看起来像这样

public static function randomElements(array $array = array('a', 'b', 'c'), $count = 1, $allowDuplicates = false)
    {
        $allKeys = array_keys($array);
        $numKeys = count($allKeys);

        if (!$allowDuplicates && $numKeys < $count) {
            throw new \LengthException(sprintf('Cannot get %d elements, only %d in array', $count, $numKeys));
        }

        $highKey = $numKeys - 1;
        $keys = $elements = array();
        $numElements = 0;

        while ($numElements < $count) {
            $num = mt_rand(0, $highKey);

            if (!$allowDuplicates) {
                if (isset($keys[$num])) {
                    continue;
                }
                $keys[$num] = true;
            }

            $elements[] = $array[$allKeys[$num]];  //THIS IS LINE 194.
            $numElements++;
        }

        return $elements;
    }

自安装Laravel以来，我没有修改它。

学生工厂正由表格工厂调用

factory(App\Form::class, $numberOfStudentsInForm)->create()->each(function ($form)
        {
            echo ("Seeding Students of Form $form->name\r\n");
            factory(App\Student::class, 30)->create(['form_id'=>$form]);
        });

学生模型看起来像这样

namespace App;

use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\SoftDeletes;

class Student extends Model
{
    use SoftDeletes;

    protected $primaryKey = "admission_number";
    public $incrementing = false;
    protected $keyType = "string";

    public function form()
    {
        return $this->belongsTo('App\Form');
    }

    public function grades()
    {
        return $this->hasMany('App\Grade');
    }

    public function delete()
    {
        return ($this->grades()->delete() && parent::delete());
    }
}

我做错了吗？