[bug] fix popularity-based recommendations on new articles that don't have

any default metrics stored on them

baseline.py

@@ -86,7 +86,11 @@ def popularity(article):
     You could replace this with a more sophisticated measure of popularity.
     """
 
-    m = article['metrics']
+    m = article.get('metrics')
+    if m is None:
+        # New articles might not have metrics saved on them yet, so the
+        # default value is just 1
+        return 1
     return max(1, m['clicks']) * max(1, (m['likes'] - m['dislikes']))