Refactor clone_button() to avoid undefined URL

netbox/utilities/templatetags/buttons.py

@@ -27,12 +27,12 @@ def _get_viewname(instance, action):
 
 @register.inclusion_tag('buttons/clone.html')
 def clone_button(instance):
-    viewname = _get_viewname(instance, 'add')
+    url = reverse(_get_viewname(instance, 'add'))
 
     # Populate cloned field values
     param_string = prepare_cloned_fields(instance)
     if param_string:
-        url = '{}?{}'.format(reverse(viewname), param_string)
+        url = f'{url}?{param_string}'
 
     return {
         'url': url,