human
Solve the following python programming problem given the following code:
@ mock.patch ('changes.jobs.sync_repo.fire_signal') 
@ mock.patch ('changes.models.Repository.get_vcs') 
@ mock.patch ('changes.config.queue.delay') 
def test_with_existing_revision(self, queue_delay, get_vcs_backend, mock_fire_signal) : 
    "
        Ensure that sync_repo creates and fires signals for existing revisions
        only if we haven't done so before and there are branches.
        " 
    vcs_backend = mock.MagicMock (spec = Vcs) 
    get_vcs_backend.return_value = vcs_backend 
    repo = self.create_repo (backend = RepositoryBackend.git) 
    existing_revision_branch_changed = RevisionResult (id = (str (3) * 40), message = 'latest commit', author = 'Example <foo@example.com>', author_date = datetime (2013, 9, 19, 22, 15, 22), branches = ['b']) 
    existing_revision_branch_changed.save (repo) 
    existing_revision_branch_changed.branches = ['b', 'c'] 
    existing_revision = RevisionResult (id = (str (4) * 40), message = 'latest commit', author = 'Example <foo@example.com>', author_date = datetime (2013, 9, 19, 22, 15, 22), branches = ['b']) 
    (r, _, _) = existing_revision.save (repo) 
    r.date_created_signal = datetime.utcnow () 
    db.session.commit () 
    existing_revision_no_branches = RevisionResult (id = (str (5) * 40), message = 'latest commit', author = 'Example <foo@example.com>', author_date = datetime (2013, 9, 19, 22, 15, 22), branches = []) 
    existing_revision_no_branches.save (repo) 
    db.session.commit () 
    def log(parent, limit, first_parent) : 
        (yield existing_revision) 
        (yield existing_revision_branch_changed) 
        (yield existing_revision_no_branches) 
        for i in range (3) : 
            (yield RevisionResult (id = (str (i) * 40), message = ('commit number' + str (i)), author = 'Example <foo@example.com>', author_date = datetime (2013, 9, 19, 22, 15, 22), branches = ['b'])) 
vcs_backend.log.side_effect = log 
    with mock.patch.object (sync_repo, 'allow_absent_from_db', True) : 
        sync_repo (repo_id = repo.id.hex, task_id =...

    
    

    Fix the buggy line: assert (r.last_update_attempt is not None)
assistant
#Here is Python program to fix the buggy line: assert (r.

assert (repo.last_update_attempt is not None)