public boolean containsKey(K key) {
        if (key == null) {
            throw new IllegalArgumentException();
        }

        int slotIndex = key.hashCode() % capacity;
        TableEntry<K, V> current = table[slotIndex];
        System.out.println();

        if (current.getKey().equals(null)) {
            return false;

        } else {

            while (current.next != null) {
                if (current.getKey().equals(key)) {
                    return true;
                } else {
                    current = current.next;
                }
            }

            return false;
        }
    }