From e497d14db01ddde77f691755ebad8227453dc05c Mon Sep 17 00:00:00 2001
From: Nuno Campos <nuno@boringbits.io>
Date: Sat, 13 Jan 2024 15:58:25 -0800
Subject: [PATCH] Fixes

---
 langgraph/graph/state.py     |  3 ++-
 langgraph/pregel/__init__.py |  7 +++++--
 langgraph/pregel/write.py    | 12 +++++++++++-
 3 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/langgraph/graph/state.py b/langgraph/graph/state.py
index c3f58edb6..3b708478a 100644
--- a/langgraph/graph/state.py
+++ b/langgraph/graph/state.py
@@ -83,7 +83,8 @@ def _coerce_state(schema: Type[Any], input: dict[str, Any]) -> dict[str, Any]:
 
 
 def _update_state(input: dict[str, Any], config: RunnableConfig):
-    ChannelWrite.do_write(config, **input)
+    if input is not None:
+        ChannelWrite.do_write(config, **input)
     return input
 
 
diff --git a/langgraph/pregel/__init__.py b/langgraph/pregel/__init__.py
index 46baeb6d4..c37a0e74c 100644
--- a/langgraph/pregel/__init__.py
+++ b/langgraph/pregel/__init__.py
@@ -563,7 +563,10 @@ def _read_channel(
     try:
         return channels[chan].get()
     except EmptyChannelError:
-        return None
+        if catch:
+            return None
+        else:
+            raise
 
 
 def _apply_writes(
@@ -604,7 +607,7 @@ def _apply_writes_from_view(
     checkpoint: Checkpoint, channels: Mapping[str, BaseChannel], values: dict[str, Any]
 ) -> None:
     for chan, value in values.items():
-        if value == channels[chan].get():
+        if value == _read_channel(channels, chan):
             continue
 
         assert isinstance(channels[chan], LastValue), (
diff --git a/langgraph/pregel/write.py b/langgraph/pregel/write.py
index 2063f5018..e44b3e3db 100644
--- a/langgraph/pregel/write.py
+++ b/langgraph/pregel/write.py
@@ -51,6 +51,11 @@ class ChannelWrite(RunnablePassthrough):
         values = [
             (chan, r.invoke(input, config) if r else input) for chan, r in self.channels
         ]
+        values = [
+            write
+            for write, chan in zip(values, self.channels)
+            if chan[1] is None or write[1] is not None
+        ]
 
         self.do_write(config, **dict(values))
 
@@ -59,10 +64,15 @@ class ChannelWrite(RunnablePassthrough):
             (chan, await r.ainvoke(input, config) if r else input)
             for chan, r in self.channels
         ]
+        values = [
+            write
+            for write, chan in zip(values, self.channels)
+            if chan[1] is None or write[1] is not None
+        ]
 
         self.do_write(config, **dict(values))
 
     @staticmethod
     def do_write(config: RunnableConfig, **values: Any) -> None:
         write: TYPE_SEND = config["configurable"][CONFIG_KEY_SEND]
-        write([(chan, val) for chan, val in values.items() if val is not None])
+        write([(chan, val) for chan, val in values.items()])