<?php

namespace Lib\Models;

use Phalcon\Mvc\Model;

class RobotCorrect extends Model
{
    public $id;
    public $title;
    public $deleted;
}

RobotCorrect::findFirst(["columns" => "title"]); 

// Result: correct behavior 

<?php

namespace Lib\Models;

use Phalcon\Mvc\Model;

class RobotError extends Model
{
    public $id;
    public $title;
    public $deleted;

    public static function findFirst($params = null): ?ModelInterface
    {
        return parent::findFirst($params);
    }
}

RobotError::findFirst(["columns" => "title"]);

// Result: error "Lib\\Models\\RobotError::findFirst(): Return value 
// must be of type ?Phalcon\\Mvc\\ModelInterface, Phalcon\\Mvc\\Model\\Row returned"