NotFoundCustomer.php

<?php

interface Customer {
    public function getEarnedDiscount(): float;

    public function addToOrdersHistory(Order $order): void;
}

// Null Customer's implementation
class NotFoundCustomer implements Customer {
    private float $DEFAULT_DISCOUNT = 1.0;

    public function getEarnedDiscount(): float {
        return $this->DEFAULT_DISCOUNT;
    }

    // Refused bequest???
    public function addToOrdersHistory(Order $order): void {
    
    }
}