Handle the case when ignored_contributors is None

Author: jtpio

github_activity/github_activity.py

@@ -467,7 +467,7 @@ def generate_activity_md(
     def ignored_user(username):
         if username in bot_users:
             return True
-        if any(fnmatch.fnmatch(username, user) for user in ignored_contributors):
+        if ignored_contributors and any(fnmatch.fnmatch(username, user) for user in ignored_contributors):
             return True
         return False