Default to 1, and code review suggestions

Author: dandavison

temporalio/nexus/_operation_context.py

@@ -561,13 +561,13 @@ def _event_reference_from_query_params(
     """
     Return an EventReference from the query params or raise ValueError.
     """
-    [reference_type] = query_params.get("referenceType", [])
+    [reference_type] = query_params.get("referenceType") or [None]
     if reference_type != "EventReference":
         raise ValueError(
             f"Expected Nexus link URL query parameter referenceType to be EventReference but got: {reference_type}"
         )
     # event type
-    [raw_event_type_name] = query_params.get(LINK_EVENT_TYPE_PARAM_NAME, [None])
+    [raw_event_type_name] = query_params.get(LINK_EVENT_TYPE_PARAM_NAME) or [None]
     if not raw_event_type_name:
         raise ValueError(f"query params do not contain event type: {query_params}")
     if raw_event_type_name.startswith("EVENT_TYPE_"):
@@ -580,8 +580,8 @@ def _event_reference_from_query_params(
         raise ValueError(f"Invalid event type name: {raw_event_type_name}")
 
     # event id
-    event_id = 0
-    [raw_event_id] = query_params.get(LINK_EVENT_ID_PARAM_NAME, [None])
+    event_id = 1
+    [raw_event_id] = query_params.get(LINK_EVENT_ID_PARAM_NAME) or [None]
     if raw_event_id:
         try:
             event_id = int(raw_event_id)