Undefined index: subscribed (by @cesag)

[bitcero]

C&P from @Cesag report (referer to bitcero/bxpress#12)

When I go to:
modules/bxpress/forum.php?id=1

I get this error:
Notice: Undefined index: subscribed in file /modules/rmcommon/templates/rmc-notifications-options.php line 16

My config:

PHP: 5.6.4-4ubuntu6.2
MYSQL: 5.6.25-0ubuntu0.15.04.1
XOOPS: 2.5.7.1
ModuleAdmin: 1.2