State the name of director for the 'Treehouse of Horror XIX' episode.
"Treehouse of Horror XIX" is the title of episode; 'director' is the role of person; name refers to person
SELECT T2.person FROM Episode AS T1 INNER JOIN Credit AS T2 ON T1.episode_id = T2.episode_id WHERE T1.title = 'Treehouse of Horror XIX' AND T2.role = 'director';