Error in seeding command in Laravel

I am using Laravel Framework 5.5.33. I am trying to run php artisan db:seed command but I am getting following error. My DatabaseSeeder.php file is like below.

<?php

use Illuminate\Database\Seeder;

class DatabaseSeeder extends Seeder
{
    public function run()
    {
        $this->call([
            ApplicantsTableSeeder::class,
            ApplicantSkillTableSeeder::class,
            SkillsTableSeeder::class,
        ]);
    }
}

I couldn't find out the Source of the error. Could anyone help me to find out the source ?