Allow null avatars from Gitlab

Not all gitlab repositories have defined owners, meaning we cannot always get an avatar_url for the namespace

Fixes 241774339/

buildtrigger/gitlabhandler.py

@@ -281,11 +281,12 @@ class GitLabBuildTrigger(BuildTriggerHandler):
         namespaces[namespace_id]['score'] = namespaces[namespace_id]['score'] + 1
       else:
         owner = repo['namespace']['name']
+        avatar_url = repo.get('owner', {}).get('avatar_url')
         namespaces[namespace_id] = {
           'personal': owner == current_user['username'],
           'id': namespace['path'],
           'title': namespace['name'],
-          'avatar_url': repo['owner']['avatar_url'],
+          'avatar_url': avatar_url,
           'score': 1,
           'url': gl_client.host + '/' + namespace['path'],
         }