public function get_items() {
		if ( null !== $this->items ) {
			return $this->items;
		}

		if ( ! $this->exists() ) {
			return false;
		}

		$this->items = [];

		$invoice_number = $this->read_invoice_number();

		$items = get_transient( self::get_transient_name( $invoice_number ) );

		if ( is_array( $items ) && ! empty( $items ) ) {
			$this->items = $items;
		}

		return $this->items;
	}