Call to undefined method Illuminate\Support\Facades\Event::newCollection()

In lumen5.5 i have implemented my factory method like this

$factory->define(App\CollegeEvent::class, function (Faker\Generator $faker) {
    return [
        'name' => randomElement(["Event1","Event2","Event4","Event3",]),
        'slug' => $faker->email,
        'category'=>randomElement(["Cat1","Cat2","Cat4","Cat3",]),
        'problem_statement'=>$faker->paragraph(),
        'description'=>$faker->paragraph(),
        'name1'=>$faker->name,
        'email1'=>$faker->email,
        'contact1'=>$faker->address,
        'name2'=>$faker->name,
        'email2'=>$faker->email,
        'contact2'=>$faker->address,
        'faculty'=>$faker->name,
    ];
}); 

also my up() method for table blue print looks like this

  public function up()
    {
        Schema::create('event', function (Blueprint $table) {
            $table->increments('id');
            $table->string('name');
            $table->string('slug');
            $table->string('category');
            $table->string('problem_statement'); //problem statement for event
            $table->text('description');
            $table->string('name1'); //cordinator1
            $table->string('email1');
            $table->string('contact1',13);
            $table->string('name2');//cordinator2
            $table->string('email2');
            $table->string('contact2',13);
            $table->string('faculty');
            $table->integer('count')->default(0);
            $table->timestamps();

        });
    }

and in DatabaseSeeder.php i have

class DatabaseSeeder extends Seeder
{
    public function run()
    {
        factory(CollegeEvent::class,10)->create();

    }
}

I don't know whether these things are important for this error but i am getting following error on running

php artisan db:seed


    [Symfony\Component\Debug\Exception\FatalThrowableError]                     
 Call to undefined methodIlluminate\Support\Facades\Event::newCollection()

via Chebli Mohamed