From 661476e88d163e224a079f683a438a19daf8889d Mon Sep 17 00:00:00 2001
From: vbarda <vadym@langchain.dev>
Date: Wed, 12 Feb 2025 17:50:25 -0800
Subject: [PATCH 1/4] langgraph: fix None handling for pydantic state updates

---
 libs/langgraph/langgraph/graph/state.py |  4 ++--
 libs/langgraph/tests/test_pregel.py     | 13 +++++++++++++
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/libs/langgraph/langgraph/graph/state.py b/libs/langgraph/langgraph/graph/state.py
index 8c93c0c1d..ac79cc497 100644
--- a/libs/langgraph/langgraph/graph/state.py
+++ b/libs/langgraph/langgraph/graph/state.py
@@ -33,7 +33,7 @@ from langgraph.channels.dynamic_barrier_value import DynamicBarrierValue, WaitFo
 from langgraph.channels.ephemeral_value import EphemeralValue
 from langgraph.channels.last_value import LastValue
 from langgraph.channels.named_barrier_value import NamedBarrierValue
-from langgraph.constants import EMPTY_SEQ, NS_END, NS_SEP, SELF, TAG_HIDDEN
+from langgraph.constants import EMPTY_SEQ, MISSING, NS_END, NS_SEP, SELF, TAG_HIDDEN
 from langgraph.errors import (
     ErrorCode,
     InvalidUpdateError,
@@ -694,7 +694,7 @@ class CompiledStateGraph(CompiledGraph):
                 return [
                     (k, getattr(input, k))
                     for k in output_keys
-                    if getattr(input, k, None) is not None
+                    if getattr(input, k, MISSING) is not MISSING
                 ]
             else:
                 msg = create_error_message(
diff --git a/libs/langgraph/tests/test_pregel.py b/libs/langgraph/tests/test_pregel.py
index ccd4fae94..6c3603499 100644
--- a/libs/langgraph/tests/test_pregel.py
+++ b/libs/langgraph/tests/test_pregel.py
@@ -6482,3 +6482,16 @@ def test_node_destinations() -> None:
             Edge(source="child", target="node_b", data="foo", conditional=True),
             Edge(source="child", target="node_c", data="bar", conditional=True),
         ] == graph.edges
+
+
+def test_pydantic_none_state_update() -> None:
+    from pydantic import BaseModel
+
+    class State(BaseModel):
+        foo: str | None
+
+    def node_a(state: State) -> State:
+        return State(foo=None)
+
+    graph = StateGraph(State).add_node(node_a).add_edge(START, "node_a").compile()
+    assert graph.invoke({"foo": ""}) == {"foo": None}

From c36323cba8e16cf90cfc14c2bb94a228c9cb6d31 Mon Sep 17 00:00:00 2001
From: vbarda <vadym@langchain.dev>
Date: Wed, 12 Feb 2025 19:17:05 -0800
Subject: [PATCH 2/4] 3.9

---
 libs/langgraph/tests/test_pregel.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libs/langgraph/tests/test_pregel.py b/libs/langgraph/tests/test_pregel.py
index 6c3603499..7e15db62f 100644
--- a/libs/langgraph/tests/test_pregel.py
+++ b/libs/langgraph/tests/test_pregel.py
@@ -6488,7 +6488,7 @@ def test_pydantic_none_state_update() -> None:
     from pydantic import BaseModel
 
     class State(BaseModel):
-        foo: str | None
+        foo: Optional[str]
 
     def node_a(state: State) -> State:
         return State(foo=None)

From b0e11ae52490a4ea75abb38ba153f50707582ff4 Mon Sep 17 00:00:00 2001
From: vbarda <vadym@langchain.dev>
Date: Wed, 12 Feb 2025 20:02:26 -0800
Subject: [PATCH 3/4] update

---
 libs/langgraph/langgraph/graph/state.py | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/libs/langgraph/langgraph/graph/state.py b/libs/langgraph/langgraph/graph/state.py
index ac79cc497..8c95b9581 100644
--- a/libs/langgraph/langgraph/graph/state.py
+++ b/libs/langgraph/langgraph/graph/state.py
@@ -691,9 +691,17 @@ class CompiledStateGraph(CompiledGraph):
                         updates.extend(_get_updates(i) or ())
                 return updates
             elif get_type_hints(type(input)):
+                # if input is a Pydantic model, only update values
+                # for the keys that have been explicitly set by the users
+                # (this is needed to avoid sending updates for fields with None defaults)
+                output_keys_ = (
+                    [k for k in output_keys if k in input.model_fields_set]
+                    if hasattr(input, "model_fields_set")
+                    else output_keys
+                )
                 return [
                     (k, getattr(input, k))
-                    for k in output_keys
+                    for k in output_keys_
                     if getattr(input, k, MISSING) is not MISSING
                 ]
             else:

From 04e8342d972271053c90aa3b96a6e8c63e2c8c3e Mon Sep 17 00:00:00 2001
From: vbarda <vadym@langchain.dev>
Date: Wed, 12 Feb 2025 20:46:12 -0800
Subject: [PATCH 4/4] pydantic v1

---
 libs/langgraph/langgraph/graph/state.py | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/libs/langgraph/langgraph/graph/state.py b/libs/langgraph/langgraph/graph/state.py
index 8c95b9581..ae8941618 100644
--- a/libs/langgraph/langgraph/graph/state.py
+++ b/libs/langgraph/langgraph/graph/state.py
@@ -694,11 +694,16 @@ class CompiledStateGraph(CompiledGraph):
                 # if input is a Pydantic model, only update values
                 # for the keys that have been explicitly set by the users
                 # (this is needed to avoid sending updates for fields with None defaults)
-                output_keys_ = (
-                    [k for k in output_keys if k in input.model_fields_set]
-                    if hasattr(input, "model_fields_set")
-                    else output_keys
-                )
+                output_keys_ = output_keys
+                # Pydantic v2
+                if hasattr(input, "model_fields_set"):
+                    output_keys_ = [
+                        k for k in output_keys if k in input.model_fields_set
+                    ]
+                # Pydantic v1
+                elif hasattr(input, "__fields_set__"):
+                    output_keys_ = [k for k in output_keys if k in input.__fields_set__]
+
                 return [
                     (k, getattr(input, k))
                     for k in output_keys_