Error raised while installing wordpress

Following Error comes when trying to install wordpress:

POST /apps
Traceback (most recent call last):
File “/usr/lib/python2.7/dist-packages/moulinette/interfaces/”, line 406, in process
ret = self.actionsmap.process(arguments, timeout=30, route=_route)
File “/usr/lib/python2.7/dist-packages/moulinette/”, line 498, in process
return func(**arguments)
File “/usr/lib/moulinette/yunohost/”, line 794, in app_install
File “/usr/lib/moulinette/yunohost/”, line 1272, in app_ssowatconf
users[username] = app_map(user=username)
File “/usr/lib/moulinette/yunohost/”, 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.