General error: 1364 Field 'registered_by' doesn't have a default value

Question

I want to add the column registered_by of my migration books with the name of the user registered in the system (it will not be possible to update this field after the record is registered, but I find the following error when registering the book:

• BookModel.php

    <?php
    
    namespace App\Models;
    
    use Illuminate\Database\Eloquent\Factories\HasFactory;
    use Illuminate\Support\Facades\Auth;
    use Illuminate\Database\Eloquent\Model;
    
    class BookModel extends Model
    {
        use HasFactory;
        public $timestamps = false;
        protected $table = 'books';
        protected $primaryKey = 'id';
        protected $fillable = ['title','author','subject','year_publication'];
        public function userName()
        {
            $this->attributes['registered_by'] = Auth::user()->name;
        }
    }