fix: handle missing blob attribute in shallow checkpoint savers (#80)

langgraph/checkpoint/redis/ashallow.py

@@ -646,12 +646,11 @@ async def _aload_pending_sends(
 
         # Extract type and blob pairs
         # Handle both direct attribute access and JSON path access
+        # Filter out documents where blob is None (similar to AsyncRedisSaver in aio.py)
         return [
-            (
-                getattr(doc, "type", ""),
-                getattr(doc, "$.blob", getattr(doc, "blob", b"")),
-            )
+            (getattr(doc, "type", ""), blob)
             for doc in sorted_writes
+            if (blob := getattr(doc, "$.blob", getattr(doc, "blob", None))) is not None
         ]
 
     async def _aload_pending_writes(

langgraph/checkpoint/redis/shallow.py

@@ -675,12 +675,11 @@ def _load_pending_sends(
 
         # Extract type and blob pairs
         # Handle both direct attribute access and JSON path access
+        # Filter out documents where blob is None (similar to RedisSaver in __init__.py)
         return [
-            (
-                getattr(doc, "type", ""),
-                getattr(doc, "$.blob", getattr(doc, "blob", b"")),
-            )
+            (getattr(doc, "type", ""), blob)
             for doc in sorted_writes
+            if (blob := getattr(doc, "$.blob", getattr(doc, "blob", None))) is not None
         ]
 
     def _make_shallow_redis_checkpoint_key_cached(

tests/test_blob_encoding_error_handling.py

@@ -248,6 +248,77 @@ def test_load_writes_empty_cases(redis_url: str) -> None:
         assert len(result2.pending_writes) == 0
 
 
+def test_empty_blob_in_pending_sends(redis_url: str) -> None:
+    """Test handling of empty byte string (b"") in pending sends as per PR #82 review suggestion."""
+    with _saver(redis_url) as saver:
+        thread_id = str(uuid4())
+
+        # Create a checkpoint
+        config: RunnableConfig = {
+            "configurable": {
+                "thread_id": thread_id,
+                "checkpoint_ns": "",
+                "checkpoint_id": "test-checkpoint",
+            }
+        }
+
+        checkpoint = create_checkpoint(
+            checkpoint=empty_checkpoint(),
+            channels={},
+            step=1,
+        )
+
+        saved_config = saver.put(
+            config, checkpoint, {"source": "test", "step": 1, "writes": {}}, {}
+        )
+
+        # Test 1: Write with empty byte string blob
+        from langgraph.constants import TASKS
+
+        # This tests the edge case where blob is b""
+        empty_blob_data = b""
+        saver.put_writes(
+            saved_config,
+            [(TASKS, empty_blob_data)],  # Empty blob
+            task_id="empty_blob_task",
+        )
+
+        # Test 2: Write with None-like values that should be handled gracefully
+        none_like_values = [
+            ("channel1", ""),  # Empty string
+            ("channel2", b""),  # Empty bytes
+            ("channel3", {}),  # Empty dict
+            ("channel4", []),  # Empty list
+        ]
+
+        saver.put_writes(
+            saved_config,
+            none_like_values,
+            task_id="empty_values_task",
+        )
+
+        # Retrieve and verify all writes are handled correctly
+        result = saver.get_tuple(saved_config)
+        assert result is not None
+
+        # Check pending writes
+        pending_writes = result.pending_writes
+
+        # Find our writes
+        empty_blob_writes = [w for w in pending_writes if w[0] == "empty_blob_task"]
+        empty_values_writes = [w for w in pending_writes if w[0] == "empty_values_task"]
+
+        # Verify empty blob is handled correctly
+        assert len(empty_blob_writes) == 1
+        assert empty_blob_writes[0][1] == TASKS
+        assert empty_blob_writes[0][2] == b""  # Should preserve empty bytes
+
+        # Verify other empty values are handled
+        assert len(empty_values_writes) == 4
+        for write in empty_values_writes:
+            assert write[2] is not None  # Should not be None even for empty values
+
+
 def test_checkpoint_with_special_characters(redis_url: str) -> None:
     """Test handling of special characters and null bytes in data.