How to use the qutebrowser.utils.qtutils.ensure_valid function in qutebrowser

def _load_url_prepare(self, url: QUrl, *,
                          emit_before_load_started: bool = True) -> None:
        qtutils.ensure_valid(url)
        if emit_before_load_started:
            self.before_load_started.emit(url)

def on_data_changed(self, idx):
        """Update view when DownloadManager data changed."""
        model_idx = self.index(idx, 0)
        qtutils.ensure_valid(model_idx)
        self.dataChanged.emit(model_idx, model_idx)

def _on_before_load_started(self, url: QUrl) -> None:
        """Adjust the title if we are going to visit a URL soon."""
        qtutils.ensure_valid(url)
        url_string = url.toDisplayString()
        log.webview.debug("Going to start loading: {}".format(url_string))
        self.title_changed.emit(url_string)

def on_url_changed(self, url):
        """Update cur_url when URL has changed."""
        qtutils.ensure_valid(url)
        self.cur_url = url
        self.url_text_changed.emit(url.toDisplayString())

def lessThan(self, lindex, rindex):
        """Custom sorting implementation.

        Prefers all items which start with self._pattern. Other than that, uses
        normal Python string sorting.

        Args:
            lindex: The QModelIndex of the left item (*left* < right)
            rindex: The QModelIndex of the right item (left < *right*)

        Return:
            True if left < right, else False
        """
        qtutils.ensure_valid(lindex)
        qtutils.ensure_valid(rindex)

        left = self.srcmodel.data(lindex)
        right = self.srcmodel.data(rindex)

        leftstart = left.startswith(self._pattern)
        rightstart = right.startswith(self._pattern)

        if leftstart and not rightstart:
            return True
        elif rightstart and not leftstart:
            return False
        elif self._sort:
            return left < right
        else:
            return False

def intelligentLessThan(self, lindex, rindex):
        """Custom sorting implementation.

        Prefers all items which start with self.pattern. Other than that, uses
        normal Python string sorting.

        Args:
            lindex: The QModelIndex of the left item (*left* < right)
            rindex: The QModelIndex of the right item (left < *right*)

        Return:
            True if left < right, else False
        """
        qtutils.ensure_valid(lindex)
        qtutils.ensure_valid(rindex)

        left_sort = self.srcmodel.data(lindex, role=completion.Role.sort)
        right_sort = self.srcmodel.data(rindex, role=completion.Role.sort)

        if left_sort is not None and right_sort is not None:
            return left_sort < right_sort

        left = self.srcmodel.data(lindex)
        right = self.srcmodel.data(rindex)

        leftstart = left.startswith(self.pattern)
        rightstart = right.startswith(self.pattern)

        if leftstart and rightstart:
            return left < right

def lessThan(self, lindex, rindex):
        """Custom sorting implementation.

        Prefers all items which start with self._pattern. Other than that, uses
        normal Python string sorting.

        Args:
            lindex: The QModelIndex of the left item (*left* < right)
            rindex: The QModelIndex of the right item (left < *right*)

        Return:
            True if left < right, else False
        """
        qtutils.ensure_valid(lindex)
        qtutils.ensure_valid(rindex)

        left = self.srcmodel.data(lindex)
        right = self.srcmodel.data(rindex)

        leftstart = left.startswith(self._pattern)
        rightstart = right.startswith(self._pattern)

        if leftstart and not rightstart:
            return True
        elif rightstart and not leftstart:
            return False
        elif self._sort:
            return left < right
        else:
            return False

def _save_tab(self, tab, active):
        """Get a dict with data for a single tab.

        Args:
            tab: The WebView to save.
            active: Whether the tab is currently active.
        """
        data = {'history': []}
        if active:
            data['active'] = True
        for idx, item in enumerate(tab.history):
            qtutils.ensure_valid(item)
            item_data = self._save_tab_item(tab, idx, item)
            if item.url().scheme() == 'qute' and item.url().host() == 'back':
                # don't add qute://back to the session file
                if item_data.get('active', False) and data['history']:
                    # mark entry before qute://back as active
                    data['history'][-1]['active'] = True
            else:
                data['history'].append(item_data)
        return data

def update_for_url(self, url: QUrl) -> typing.Set[str]:
        """Update settings customized for the given tab.

        Return:
            A set of settings which actually changed.
        """
        qtutils.ensure_valid(url)
        changed_settings = set()
        for values in config.instance:
            if not values.opt.supports_pattern:
                continue

            value = values.get_for_url(url, fallback=False)

            changed = self._update_setting(values.opt.name, value)
            if changed:
                log.config.debug("Changed for {}: {} = {}".format(
                    url.toDisplayString(), values.opt.name, value))
                changed_settings.add(values.opt.name)

        return changed_settings

def get_by_qurl(self, url):
        """Look up a quickmark by QUrl, returning its name.

        Takes O(n) time, where n is the number of quickmarks.
        Use a name instead where possible.
        """
        qtutils.ensure_valid(url)
        urlstr = url.toString(QUrl.RemovePassword | QUrl.FullyEncoded)

        try:
            index = list(self.marks.values()).index(urlstr)
            key = list(self.marks.keys())[index]
        except ValueError:
            raise DoesNotExistError(
                "Quickmark for '{}' not found!".format(urlstr))
        return key