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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_asset_form_for_update(self, asset_id=None):
 """Gets the asset form for updating an existing asset. A new asset form should be requested for each update transaction. :param asset_id: the ``Id`` of the ``Asset`` :type asset_id: ``osid.id.Id`` :return: the asset form :rtype: ``osid.repository.AssetForm`` :raise: ``NotFound`` -- ``asset_id`` is not found :raise: ``NullArgument`` -- ``asset_id`` is null :raise: ``OperationFailed`` -- unable to complete request :raise: ``PermissionDenied`` -- authorization failure *compliance: mandatory -- This method must be implemented.* """

        if asset_id is None:
            raise NullArgument()
        try:
            url_path = construct_url('assets',
                                     bank_id=self._catalog_idstr,
                                     asset_id=asset_id)
            asset = objects.Asset(self._get_request(url_path))
        except Exception:
            raise
        asset_form = objects.AssetForm(asset._my_map)
        self._forms[asset_form.get_id().get_identifier()] = not UPDATED
        return asset_form