Error when VisitsSummary plugin is deactivated (no replies)

The following error message is shown in 'Visitors -> Location&Provider -> Visitor Map' when the plugin VisitsSummary is deactivated. Everything is fine as long as this plugin is active.

There is an error. Please report the message (Piwik 1.11.1) and full backtrace in the Piwik forums (please do a Search first as it might have been reported already!).

Notice: Undefined index: nb_visits in /var/www/vhosts/www.domainname.de/piwik/plugins/UserCountryMap/Controller.php on line 85

Backtrace -->

#0 Piwik_ErrorHandler(...) called at [/var/www/vhosts/www.domainname.de/piwik/plugins/UserCountryMap/Controller.php:85]
#1 Piwik_UserCountryMap_Controller->visitorMap(...) called at [:]
#2 call_user_func_array(...) called at [/var/www/vhosts/www.domainname.de/piwik/core/FrontController.php:136]
#3 Piwik_FrontController->dispatch(...) called at [/var/www/vhosts/www.domainname.de/piwik/core/FrontController.php:158]
#4 Piwik_FrontController->fetchDispatch(...) called at [/var/www/vhosts/www.domainname.de/piwik/plugins/UserCountryMap/UserCountryMap.php:41]
#5 Piwik_UserCountryMap::insertMapInLocationReport(...) called at [:]
#6 call_user_func_array(...) called at [/var/www/vhosts/www.domainname.de/piwik/libs/Event/Dispatcher.php:284]
#7 Event_Dispatcher->postNotification(...) called at [/var/www/vhosts/www.domainname.de/piwik/core/PluginsManager.php:722]
#8 Piwik_PostEvent(...) called at [/var/www/vhosts/www.domainname.de/piwik/core/SmartyPlugins/function.postEvent.php:40]
#9 smarty_function_postEvent(...) called at [/var/www/vhosts/www.domainname.de/piwik/tmp/templates_c/%%7A^7AC^7AC033CF%%index.tpl.php:7]
#10 include(...) called at [/var/www/vhosts/www.domainname.de/piwik/libs/Smarty/Smarty.class.php:1263]
#11 Smarty->fetch(...) called at [/var/www/vhosts/www.domainname.de/piwik/core/View.php:127]
#12 Piwik_View->render(...) called at [/var/www/vhosts/www.domainname.de/piwik/plugins/UserCountry/Controller.php:30]
#13 Piwik_UserCountry_Controller->index(...) called at [:]
#14 call_user_func_array(...) called at [/var/www/vhosts/www.domainname.de/piwik/core/FrontController.php:136]
#15 Piwik_FrontController->dispatch(...) called at [/var/www/vhosts/www.domainname.de/piwik/index.php:52]

Maybe it is the same issue as [forum.piwik.org]

Best regards