catch resolver failure due to bad URLs

judgments/templatetags/navigation_tags.py

@@ -1,5 +1,5 @@
 from django import template
-from django.urls import resolve
+from django.urls import Resolver404, resolve
 
 register = template.Library()
 
@@ -8,7 +8,12 @@
 def navigation_item_class(context, path):
     request = context.get("request")
 
-    if request and resolve(request.path_info).url_name == path:
+    try:
+        request_path = resolve(request.path_info).url_name
+    except Resolver404:
+        request_path = None
+
+    if request and request_path and request_path == path:
         return "govuk-header__navigation-item govuk-header__navigation-item--active"
 
     return "govuk-header__navigation-item"