SQLSTATE[42883]: Undefined function: 7 ERROR: operator does not exist: character varying = integer

Hi , I use postgresql and i have three table :

Habilitation

code              - string(225)
code_menu  - string(225) 
code_sub_menu  - string(225) 
name             - string(225)

menu

code              - string(225)
name             - string(225)

submenu

code              - string(225)
name             - string(225)

I want to show habilitations with their menu and sub-menu using Eloquent , when i try :

Habilitation::with(['menu','submenu'])->get();

i get this error :

Illuminate\Database\QueryException
SQLSTATE[42883]: Undefined function: 7 ERROR: operator does not exist: character varying = integer LINE 1: select * from "menu" where "menu"."code" in (0, 0, 0, 0) ^ HINT: No operator matches the given name and argument types. You might need to add explicit type casts. (SQL: select * from "menu" where "menu"."code" in (0, 0, 0, 0)) 

My models :

class Menu extends Model
{
    protected $table = "menu";
    public $primaryKey = "code";
    public $timestamps = false;

    protected $casts = [
        'code' => 'string',
    ];

    public function submenu()
    {
        return $this->hasMany('App\Models\SubMenu','code');
    }

    public function habilitation()
    {
        return $this->hasMany('App\Models\Habilitation','code');
    }
}

class SubMenu extends Model
{
    protected $table = "submenu";
    public $primaryKey = "code";
    public $timestamps = false;

    protected $casts = [
        'code' => 'string',
    ];

    public function menu()
    {
        return $this->belongsTo('App\Models\SubMenu','code');
    }

    public function habilitation()
    {
        return $this->hasMany('App\Models\Habilitation','code');
    }

}

class Habilitation extends Model
{
    protected $table = "habilitation";
    public $primaryKey = "code";
    public $timestamps = false;

    protected $fillable = [
        'code', ''code_menu','code_sub_menu'
    ];

    protected $casts = [
        'code' => 'string',
        'code_menu' => 'string',
        'code_sub_menu' => 'string'
    ];

    public function menu()
    {
        return $this->belongsTo('App\Models\Menu','code_menu','code');
    }

    public function submenu()
    {
        return $this->belongsTo('App\Models\SubMenu');
    }

}

someone could help me ? thank you in advance