When accessing a dashboard (created on template) containing a Classic Graph widget, an admin-level user encounters the error message: "System error occurred. Please contact Zabbix administrator."

Steps to reproduce:
1. Create a template and add a dashboard with a Classic Graph widget.
2. Link the template to a host X.
3. Create a user group with read or read-write permissions for host X.
4. Create an admin user and assign them to the user group from step 3.
5. Log in with the newly created admin user.
6. Navigate to Monitoring → Hosts → Dashboard.

Result:

Undefined array key 0 [zabbix.php:17 > require_once() -> ZBase>run() > ZBase>processRequest() > CController>run() > Widgets\Graph\Actions\WidgetView>doAction() > CConfigFile>
{closure}() in widgets/graph/actions/WidgetView.php:112]
Trying to access array offset on null [zabbix.php:17 > require_once() -> ZBase>run() > ZBase>processRequest() > CController>run() > Widgets\Graph\Actions\WidgetView>doAction() > CConfigFile>{closure}
() in widgets/graph/actions/WidgetView.php:112]

Expected:
The Classic Graph widget should load and display the relevant monitoring data for host X or show "no permissions" notification.