diff --git a/cartridges/importer/location.py b/cartridges/importer/location.py
index 2ff6a64..1d70466 100644
--- a/cartridges/importer/location.py
+++ b/cartridges/importer/location.py
@@ -16,7 +16,7 @@ class LocationSubPath(NamedTuple):
 
 
 class UnresolvableLocationError(Exception):
-    def __init__(self, optional):
+    def __init__(self, optional: Optional[bool] = False):
         self.optional = optional