Fix notifications building from JSON

Sometimes (like in welcome messages), notifications don't have a
'title' property, so we shouldn't assume there is one.

Bug: T139015
Change-Id: I83e480d04e8e09aa9bcb5edef4f56b47d150e199
(cherry picked from commit d387ab2)

pywikibot/echo.py

@@ -27,8 +27,10 @@ def fromJSON(cls, site, data):
         notif.category = data['category']
         notif.timestamp = pywikibot.Timestamp.fromtimestampformat(data['timestamp']['mw'])
 
-        # TODO: use 'namespace-key' + 'text' ?
-        notif.page = pywikibot.Page(site, data['title']['full'])
+        if 'title' in data and 'full' in data['title']:
+            notif.page = pywikibot.Page(site, data['title']['full'])
+        else:
+            notif.page = None
 
         if 'agent' in data and 'name' in data['agent']:
             notif.agent = pywikibot.User(site, data['agent']['name'])