Don't return a None value, so we'll use default if set

src/documents/templating/filepath.py

@@ -82,7 +82,7 @@ def get_cf_value(
     name: str,
     default: str | None = None,
 ) -> str | None:
-    if name in custom_field_data:
+    if name in custom_field_data and custom_field_data[name]["value"] is not None:
         return custom_field_data[name]["value"]
     elif default is not None:
         return default