'Copy the subtree rooted at source_location and mark the copies as draft.
Args:
location: the location of the source (its revision must be None)
user_id: the ID of the user doing the operation
Raises:
InvalidVersionError: if the source can not be made into a draft
ItemNotFoundError: if the source does not exist'

def convert_to_draft(self, location, user_id):

    self._convert_to_draft(location, user_id, ignore_if_draft=True)
    return self.get_item(location)
