Handle empty async export state

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot-Session: 76f2163a-0773-4889-b627-1bd4e5c7bea0

Author: andystaples

durabletask/extensions/history_export/client.py

@@ -534,7 +534,7 @@ async def get_job(self, job_id: str) -> ExportJobDescription | None:
         if meta is None:
             return None
         state = meta.get_typed_state()
-        if not isinstance(state, dict):
+        if not isinstance(state, dict) or not state:
             return None
         return ExportJobDescription.from_state_dict(job_id, cast("dict[str, Any]", state))
 

tests/durabletask/extensions/history_export/test_client.py

@@ -13,6 +13,7 @@
 import gzip
 import json
 import threading
+from unittest.mock import AsyncMock, MagicMock
 from datetime import datetime, timedelta, timezone
 
 import pytest
@@ -175,6 +176,16 @@ async def test_async_client_create_list_wait_and_delete(
         assert await export_client.get_job(desc.job_id) is None
 
 
+async def test_async_client_get_job_returns_none_for_empty_state(writer):
+    dt_client = MagicMock()
+    metadata = MagicMock()
+    metadata.get_typed_state.return_value = {}
+    dt_client.get_entity = AsyncMock(return_value=metadata)
+    export_client = AsyncExportHistoryClient(dt_client, writer)
+
+    assert await export_client.get_job("empty-state") is None
+
+
 def test_get_job_returns_none_for_unknown_id(export_client):
     assert export_client.get_job("does-not-exist") is None