Fix flasy return from task

libs/langgraph/langgraph/pregel/io.py

@@ -10,6 +10,7 @@ from langgraph.constants import (
     EMPTY_SEQ,
     ERROR,
     INTERRUPT,
+    MISSING,
     NULL_TASK_ID,
     RESUME,
     RETURN,
@@ -173,7 +174,8 @@ def map_output_updates(
         return
     updated: list[tuple[str, Any]] = []
     for task, writes in output_tasks:
-        if rtn := next((value for chan, value in writes if chan == RETURN), None):
+        rtn = next((value for chan, value in writes if chan == RETURN), MISSING)
+        if rtn is not MISSING:
             updated.append((task.name, rtn))
         elif isinstance(output_channels, str):
             updated.extend(

libs/langgraph/langgraph/pregel/runner.py

@@ -25,6 +25,7 @@ from langgraph.constants import (
     CONFIG_KEY_SEND,
     ERROR,
     INTERRUPT,
+    MISSING,
     NO_WRITES,
     PUSH,
     RESUME,
@@ -113,9 +114,15 @@ class PregelRunner:
                     elif next_task.writes:
                         # if it already ran, return the result
                         fut = concurrent.futures.Future()
-                        if val := next(v for c, v in next_task.writes if c == RETURN):
+                        if (
+                            val := next(
+                                (v for c, v in next_task.writes if c == RETURN), MISSING
+                            )
+                        ) and val is not MISSING:
                             fut.set_result(val)
-                        elif exc := next(v for c, v in next_task.writes if c == ERROR):
+                        elif exc := next(
+                            (v for c, v in next_task.writes if c == ERROR), None
+                        ):
                             fut.set_exception(
                                 exc
                                 if isinstance(exc, BaseException)
@@ -299,9 +306,15 @@ class PregelRunner:
                     elif next_task.writes:
                         # if it already ran, return the result
                         fut = asyncio.Future()
-                        if val := next(v for c, v in next_task.writes if c == RETURN):
+                        if (
+                            val := next(
+                                (v for c, v in next_task.writes if c == RETURN), MISSING
+                            )
+                        ) and val is not MISSING:
                             fut.set_result(val)
-                        elif exc := next(v for c, v in next_task.writes if c == ERROR):
+                        elif exc := next(
+                            (v for c, v in next_task.writes if c == ERROR), None
+                        ):
                             fut.set_exception(
                                 exc
                                 if isinstance(exc, BaseException)

libs/langgraph/tests/test_pregel.py

@@ -5273,8 +5273,8 @@ def test_falsy_return_from_task() -> None:
     @entrypoint(checkpointer=checkpointer)
     def graph(state: dict) -> dict:
         """React tool."""
-        task_result = falsy_task().result()
-        human_value = interrupt("test")
+        falsy_task().result()
+        interrupt("test")
 
     configurable = {"configurable": {"thread_id": uuid.uuid4()}}
     graph.invoke({"a": 5}, configurable)

libs/langgraph/tests/test_pregel_async.py

@@ -6693,3 +6693,22 @@ async def test_multiple_updates() -> None:
         {"node_a": [{"foo": "a1"}, {"foo": "a2"}]},
         {"node_b": {"foo": "b"}},
     ]
+
+
+async def test_falsy_return_from_task() -> None:
+    """Test with a falsy return from a task."""
+    checkpointer = MemorySaver()
+
+    @task
+    async def falsy_task() -> bool:
+        return False
+
+    @entrypoint(checkpointer=checkpointer)
+    async def graph(state: dict) -> dict:
+        """React tool."""
+        await falsy_task()
+        interrupt("test")
+
+    configurable = {"configurable": {"thread_id": uuid.uuid4()}}
+    await graph.ainvoke({"a": 5}, configurable)
+    await graph.ainvoke(Command(resume="123"), configurable)