october cms "SQLSTATE[HY000]: General error: 1364 Field does not have a default value

I'm trying to update a model but it is complaing the field does not have a default value, but I am setting one before saving it in the boot method of my plugin see code below where I have outlined the details,I am not sure why it thinks there is no value. Any help greatly appreciated

plugin.php

    public function boot()
{


//  RainlabUser::extend(function ($model) {
//      $model->hasOne['newsletter'] = [
//          'CG\Newsletter\Models\Newsletter', 'table' =>
//          'cg_newsletter', 'key' => 'user_id'
//      ];  
//    });

    Event::listen('eloquent.updating: RainLab\User\Models\User', function(){
            $data = post();

           if (array_key_exists('email', $data)) {  

             Log::debug(__FUNCTION__,[$data['email']]);                     
             $user = RainlabUser::findByEmail($data['email']);

             Log::debug(__FUNCTION__,[$user->id]);  
             $newsletter = new Newsletter();
             $newsletter->isSubscribed = 1;
             $newsletter->user_id = $user->id;


             Log::debug(__FUNCTION__,[$newsletter]);
             $newsletter->save();

           }
    });



}

model

use Model;

/**
 * Model
 */
class Newsletter extends Model {    

    /**
    * Indicates if the model should be timestamped.
    *
    * @var bool
    */
    public $timestamps = false;

    protected $primaryKey = 'id';

    /** 
     *
     * @var string The database table used by the model.
     */
    public $table = 'cg_newsletter';


    public $belongsTwo = [
        'user' => ['rainlab/user/models/user']
    ];

    public $isSubscribed;


}

via Chebli Mohamed