diff --git a/ox/imdb.py b/ox/imdb.py
index e43d7ee..40e7eec 100644
--- a/ox/imdb.py
+++ b/ox/imdb.py
@@ -307,7 +307,7 @@ def getMovieExternalReviews(imdbId):
 
 def getMovieReleaseDate(imdbId):
     releasedates = getMovieReleaseDates(imdbId)
-    first_release = ''
+    first_release = None
     for r in releasedates:
         if not first_release or r[1] < first_release:
             first_release = r[1]