Return inventory information and collect if not available.

def inventory_text(self):
        """Return inventory information and collect if not available."""
        if self._inventory_text is None:
            self.chain.connection.log("Collecting inventory information")
            self._inventory_text = self.driver.get_inventory_text()
            if self._inventory_text:
                self.chain.connection.log("Inventory info collected")
            else:
                self.chain.connection.log("Inventory info not collected")
        return self._inventory_text