Error raised while installing wordpress

Following Error comes when trying to install wordpress:

Action
POST /apps
{“locale”:“en”,“app”:“wordpress”,“args”:“domain=subdomain.testdomain.com&path=%2Ftestdomain&admin=testadmin&language=en_US&is_public=1&multisite=0”,“label”:“testdomain”}
Traceback
Traceback (most recent call last):
File “/usr/lib/python2.7/dist-packages/moulinette/interfaces/api.py”, line 406, in process
ret = self.actionsmap.process(arguments, timeout=30, route=_route)
File “/usr/lib/python2.7/dist-packages/moulinette/actionsmap.py”, line 498, in process
return func(**arguments)
File “/usr/lib/moulinette/yunohost/app.py”, line 794, in app_install
app_ssowatconf(auth)
File “/usr/lib/moulinette/yunohost/app.py”, line 1272, in app_ssowatconf
users[username] = app_map(user=username)
File “/usr/lib/moulinette/yunohost/app.py”, line 420, in app_map
result[domain + path] = app_settings[‘label’]
TypeError: cannot concatenate ‘str’ and ‘NoneType’ objects

Iam using the Debian stretch based yunohost in a cloud server.