add nullable field

Author: giancarloromeo

services/director-v2/src/simcore_service_director_v2/models/dynamic_services_scheduler.py

@@ -476,11 +476,11 @@ def get_proxy_endpoint(self) -> AnyHttpUrl:
     ] = None
 
     product_api_base_url: Annotated[
-        AnyHttpUrl,
+        AnyHttpUrl | None,
         Field(
-            description="Base URL for the current product's API",
+            description="Base URL for the current product's API.",
         ),
-    ]
+    ] = None
 
     @classmethod
     def from_http_request(