Fixes #13727: Fix exception when viewing rendered config for VM witho…

…ut a role assigned

netbox/dcim/models/mixins.py

@@ -69,7 +69,7 @@ def get_config_template(self):
         """
         if self.config_template:
             return self.config_template
-        if self.role.config_template:
+        if self.role and self.role.config_template:
             return self.role.config_template
         if self.platform and self.platform.config_template:
             return self.platform.config_template