Not being able to acces an atribute that exists PHP

I'm trying to access the attribute expireDate that exists in my classes Food and Drink but when I try to access it through a common method of the classes, it gives the error Warning: Undefined property: Drink::$expireDate. Even if before and after the invocation of said method I print the __toString of the instances and the attribute I'm talking about is there.

for ($i = 0; $i < count($this -> slots); $i++) {
                for ($j = 0; $j < count($this -> slots[$i]); $j++) {
                    if ($this->slots[$i][$j] != null) {
                        if (get_class($this->slots[$i][$j]) == "Food" || get_class($this->slots[$i][$j]) == "Drink") {
                            echo $this -> slots[$i][$j]-> expireDate;  <-- Giving the error on this line
                        }
                     }
                 }
}

When using the method the output is:

Weight: 7 Price: 20 Is new: true Name: RedBull Expire Date: 06/10/2012 Tax: 30 Is alcoholic: 1Volume: 200
Weight: 1 Price: 25 Is new: true Name: Absolut Vodka Expire Date: 06/10/300 Tax: 21 Is alcoholic: 1Volume: 1000
Weight: 2 Price: 2 Is new: true Name: Coca Cola Expire Date: 06/10/2020 Tax: 5 Is alcoholic: Volume: 2000
Weight: 4 Price: 10 Is new: true Name: Arroz Integral Expire Date: 06/10/2026 Tax: 10 Type: Cereal,Seco
Weight: 6 Price: 4 Is new: true Name: Tomate Frito Expire Date: 12/06/2020 Tax: 10 Type: Salsa,Verduras
Weight: 4 Price: 2.5 Is new: true Name: Iogurt Expire Date: 07/10/2022 Tax: 10 Type: Lacteo,Postre
Weight: 4 Price: 18 Is new: true Name: pañuelo Warranty Due Date: 04/10/2024Purchase Date: 10/04/2022Tax: 21
Weight: 400 Price: 10200 Is new: true Name: coche Warranty Due Date: Purchase Date: 10/04/2022Tax: 21
Weight: 150 Price: 4300 Is new: true Name: moto Warranty Due Date: Purchase Date: 10/04/2022Tax: 21


Warning: Undefined property: Drink::$expireDate in C:\xampp\htdocs\M07-php\UF1\Practica\Models\Warehouse.php on line 141

Warning: Undefined property: Drink::$expireDate in C:\xampp\htdocs\M07-php\UF1\Practica\Models\Warehouse.php on line 141

Warning: Undefined property: Drink::$expireDate in C:\xampp\htdocs\M07-php\UF1\Practica\Models\Warehouse.php on line 141

Warning: Undefined property: Food::$expireDate in C:\xampp\htdocs\M07-php\UF1\Practica\Models\Warehouse.php on line 141

Warning: Undefined property: Food::$expireDate in C:\xampp\htdocs\M07-php\UF1\Practica\Models\Warehouse.php on line 141

Warning: Undefined property: Food::$expireDate in C:\xampp\htdocs\M07-php\UF1\Practica\Models\Warehouse.php on line 141

Weight: 7 Price: 20 Is new: true Name: RedBull Expire Date: 06/10/2012 Tax: 30 Is alcoholic: 1Volume: 200
Weight: 1 Price: 25 Is new: true Name: Absolut Vodka Expire Date: 06/10/300 Tax: 21 Is alcoholic: 1Volume: 1000
Weight: 2 Price: 2 Is new: true Name: Coca Cola Expire Date: 06/10/2020 Tax: 5 Is alcoholic: Volume: 2000
Weight: 4 Price: 10 Is new: true Name: Arroz Integral Expire Date: 06/10/2026 Tax: 10 Type: Cereal,Seco
Weight: 6 Price: 4 Is new: true Name: Tomate Frito Expire Date: 12/06/2020 Tax: 10 Type: Salsa,Verduras
Weight: 4 Price: 2.5 Is new: true Name: Iogurt Expire Date: 07/10/2022 Tax: 10 Type: Lacteo,Postre
Weight: 4 Price: 18 Is new: true Name: pañuelo Warranty Due Date: 04/10/2024Purchase Date: 10/04/2022Tax: 21
Weight: 400 Price: 10200 Is new: true Name: coche Warranty Due Date: Purchase Date: 10/04/2022Tax: 21
Weight: 150 Price: 4300 Is new: true Name: moto Warranty Due Date: Purchase Date: 10/04/2022Tax: 21

source https://stackoverflow.com/questions/73965310/not-being-able-to-acces-an-atribute-that-exists-php