def get_cached_form(self) -> FormElement:
        """Get form which has been already selected.

        Returns None if form has not been selected yet.

        It is for testing mainly. To not trigger pylint warnings about
        accessing protected element.
        """
        if self._lxml_form is None:
            raise ValueError("Requested form does not exist")
        assert isinstance(self._lxml_form, FormElement)
        return self._lxml_form
Get form which has been already selected.

        Returns None if form has not been selected yet.

        It is for testing mainly. To not trigger pylint warnings about
        accessing protected element.
        
grab/document.py