Gets the asset content form for updating an existing asset content.

        A new asset content form should be requested for each update
        transaction.

        arg:    asset_content_id (osid.id.Id): the ``Id`` of the
                ``AssetContent``
        return: (osid.repository.AssetContentForm) - the asset content
                form
        raise:  NotFound - ``asset_content_id`` is not found
        raise:  NullArgument - ``asset_content_id`` is ``null``
        raise:  OperationFailed - unable to complete request
        *compliance: mandatory -- This method must be implemented.*

def get_asset_content_form_for_update(self, asset_content_id):
        """Gets the asset content form for updating an existing asset content.

        A new asset content form should be requested for each update
        transaction.

        arg:    asset_content_id (osid.id.Id): the ``Id`` of the
                ``AssetContent``
        return: (osid.repository.AssetContentForm) - the asset content
                form
        raise:  NotFound - ``asset_content_id`` is not found
        raise:  NullArgument - ``asset_content_id`` is ``null``
        raise:  OperationFailed - unable to complete request
        *compliance: mandatory -- This method must be implemented.*

        """
        # Implemented from template for
        # osid.repository.AssetAdminSession.get_asset_content_form_for_update_template
        from dlkit.abstract_osid.id.primitives import Id as ABCId
        from .objects import AssetContentForm
        collection = JSONClientValidated('repository',
                                         collection='Asset',
                                         runtime=self._runtime)
        if not isinstance(asset_content_id, ABCId):
            raise errors.InvalidArgument('the argument is not a valid OSID Id')
        document = collection.find_one({'assetContents._id': ObjectId(asset_content_id.get_identifier())})
        for sub_doc in document['assetContents']:  # There may be a MongoDB shortcut for this
            if sub_doc['_id'] == ObjectId(asset_content_id.get_identifier()):
                result = sub_doc
        obj_form = AssetContentForm(
            osid_object_map=result,
            runtime=self._runtime,
            proxy=self._proxy)
        obj_form._for_update = True
        self._forms[obj_form.get_id().get_identifier()] = not UPDATED
        return obj_form