From ca89f69dcdd8d62ae02780c3f168fba912e1a0ef Mon Sep 17 00:00:00 2001
From: Tat Dat Duong <david@duong.cz>
Date: Tue, 15 Jul 2025 17:44:22 +0200
Subject: [PATCH 1/2] feat[core]: message type assertions should accept null |
 undefined

---
 langchain-core/src/messages/ai.ts       |  8 ++++++--
 langchain-core/src/messages/base.ts     |  5 +++--
 langchain-core/src/messages/chat.ts     | 15 ++++++++++++---
 langchain-core/src/messages/function.ts |  8 ++++++--
 langchain-core/src/messages/human.ts    |  8 ++++++--
 langchain-core/src/messages/system.ts   |  8 ++++++--
 langchain-core/src/messages/tool.ts     | 15 ++++++++++++---
 7 files changed, 51 insertions(+), 16 deletions(-)

diff --git a/langchain-core/src/messages/ai.ts b/langchain-core/src/messages/ai.ts
index 61729e29c1a1..9d69ed4eeaa8 100644
--- a/langchain-core/src/messages/ai.ts
+++ b/langchain-core/src/messages/ai.ts
@@ -219,11 +219,15 @@ export class AIMessage extends BaseMessage {
   }
 }
 
-export function isAIMessage(x: BaseMessage): x is AIMessage {
+export function isAIMessage(x: BaseMessage | null | undefined): x is AIMessage {
+  if (x == null) return false;
   return x._getType() === "ai";
 }
 
-export function isAIMessageChunk(x: BaseMessageChunk): x is AIMessageChunk {
+export function isAIMessageChunk(
+  x: BaseMessageChunk | null | undefined
+): x is AIMessageChunk {
+  if (x == null) return false;
   return x._getType() === "ai";
 }
 
diff --git a/langchain-core/src/messages/base.ts b/langchain-core/src/messages/base.ts
index f6b47a38c6b0..679e9e847178 100644
--- a/langchain-core/src/messages/base.ts
+++ b/langchain-core/src/messages/base.ts
@@ -544,13 +544,14 @@ export type BaseMessageLike =
   | SerializedConstructor;
 
 export function isBaseMessage(
-  messageLike?: unknown
+  messageLike: unknown | null | undefined
 ): messageLike is BaseMessage {
+  if (messageLike == null) return false;
   return typeof (messageLike as BaseMessage)?._getType === "function";
 }
 
 export function isBaseMessageChunk(
-  messageLike?: unknown
+  messageLike: unknown | null | undefined
 ): messageLike is BaseMessageChunk {
   return (
     isBaseMessage(messageLike) &&
diff --git a/langchain-core/src/messages/chat.ts b/langchain-core/src/messages/chat.ts
index 376c05cceb84..634c7ec0784d 100644
--- a/langchain-core/src/messages/chat.ts
+++ b/langchain-core/src/messages/chat.ts
@@ -45,7 +45,10 @@ export class ChatMessage
     return "generic";
   }
 
-  static isInstance(message: BaseMessage): message is ChatMessage {
+  static isInstance(
+    message: BaseMessage | null | undefined
+  ): message is ChatMessage {
+    if (message == null) return false;
     return message._getType() === "generic";
   }
 
@@ -109,10 +112,16 @@ export class ChatMessageChunk extends BaseMessageChunk {
   }
 }
 
-export function isChatMessage(x: BaseMessage): x is ChatMessage {
+export function isChatMessage(
+  x: BaseMessage | null | undefined
+): x is ChatMessage {
+  if (x == null) return false;
   return x._getType() === "generic";
 }
 
-export function isChatMessageChunk(x: BaseMessageChunk): x is ChatMessageChunk {
+export function isChatMessageChunk(
+  x: BaseMessageChunk | null | undefined
+): x is ChatMessageChunk {
+  if (x == null) return false;
   return x._getType() === "generic";
 }
diff --git a/langchain-core/src/messages/function.ts b/langchain-core/src/messages/function.ts
index 7e3455b8ca51..7b6f6dacdf3d 100644
--- a/langchain-core/src/messages/function.ts
+++ b/langchain-core/src/messages/function.ts
@@ -74,12 +74,16 @@ export class FunctionMessageChunk extends BaseMessageChunk {
   }
 }
 
-export function isFunctionMessage(x: BaseMessage): x is FunctionMessage {
+export function isFunctionMessage(
+  x: BaseMessage | null | undefined
+): x is FunctionMessage {
+  if (x == null) return false;
   return x._getType() === "function";
 }
 
 export function isFunctionMessageChunk(
-  x: BaseMessageChunk
+  x: BaseMessageChunk | null | undefined
 ): x is FunctionMessageChunk {
+  if (x == null) return false;
   return x._getType() === "function";
 }
diff --git a/langchain-core/src/messages/human.ts b/langchain-core/src/messages/human.ts
index ae55eb0c62ef..a58e41fa1b3c 100644
--- a/langchain-core/src/messages/human.ts
+++ b/langchain-core/src/messages/human.ts
@@ -76,12 +76,16 @@ export class HumanMessageChunk extends BaseMessageChunk {
   }
 }
 
-export function isHumanMessage(x: BaseMessage): x is HumanMessage {
+export function isHumanMessage(
+  x: BaseMessage | null | undefined
+): x is HumanMessage {
+  if (x == null) return false;
   return x.getType() === "human";
 }
 
 export function isHumanMessageChunk(
-  x: BaseMessageChunk
+  x: BaseMessageChunk | null | undefined
 ): x is HumanMessageChunk {
+  if (x == null) return false;
   return x.getType() === "human";
 }
diff --git a/langchain-core/src/messages/system.ts b/langchain-core/src/messages/system.ts
index 3395dc284b89..6f8337137ce9 100644
--- a/langchain-core/src/messages/system.ts
+++ b/langchain-core/src/messages/system.ts
@@ -75,12 +75,16 @@ export class SystemMessageChunk extends BaseMessageChunk {
   }
 }
 
-export function isSystemMessage(x: BaseMessage): x is SystemMessage {
+export function isSystemMessage(
+  x: BaseMessage | null | undefined
+): x is SystemMessage {
+  if (x == null) return false;
   return x._getType() === "system";
 }
 
 export function isSystemMessageChunk(
-  x: BaseMessageChunk
+  x: BaseMessageChunk | null | undefined
 ): x is SystemMessageChunk {
+  if (x == null) return false;
   return x._getType() === "system";
 }
diff --git a/langchain-core/src/messages/tool.ts b/langchain-core/src/messages/tool.ts
index 9dfe48f6ad76..a199a3cb2816 100644
--- a/langchain-core/src/messages/tool.ts
+++ b/langchain-core/src/messages/tool.ts
@@ -115,7 +115,10 @@ export class ToolMessage extends BaseMessage implements DirectToolOutput {
     return "tool";
   }
 
-  static isInstance(message: BaseMessage): message is ToolMessage {
+  static isInstance(
+    message: BaseMessage | null | undefined
+  ): message is ToolMessage {
+    if (message == null) return false;
     return message._getType() === "tool";
   }
 
@@ -314,10 +317,16 @@ export function defaultToolCallParser(
   return [toolCalls, invalidToolCalls];
 }
 
-export function isToolMessage(x: BaseMessage): x is ToolMessage {
+export function isToolMessage(
+  x: BaseMessage | null | undefined
+): x is ToolMessage {
+  if (x == null) return false;
   return x._getType() === "tool";
 }
 
-export function isToolMessageChunk(x: BaseMessageChunk): x is ToolMessageChunk {
+export function isToolMessageChunk(
+  x: BaseMessageChunk | null | undefined
+): x is ToolMessageChunk {
+  if (x == null) return false;
   return x._getType() === "tool";
 }

From 8dc96d784c1b33bd42c00b5db918341e17f16c64 Mon Sep 17 00:00:00 2001
From: Tat Dat Duong <david@duong.cz>
Date: Tue, 15 Jul 2025 20:45:12 +0200
Subject: [PATCH 2/2] Use !x instead

---
 langchain-core/src/messages/ai.ts       | 4 ++--
 langchain-core/src/messages/base.ts     | 2 +-
 langchain-core/src/messages/chat.ts     | 6 +++---
 langchain-core/src/messages/function.ts | 4 ++--
 langchain-core/src/messages/human.ts    | 4 ++--
 langchain-core/src/messages/system.ts   | 4 ++--
 langchain-core/src/messages/tool.ts     | 2 +-
 7 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/langchain-core/src/messages/ai.ts b/langchain-core/src/messages/ai.ts
index 9d69ed4eeaa8..119e61a94042 100644
--- a/langchain-core/src/messages/ai.ts
+++ b/langchain-core/src/messages/ai.ts
@@ -220,14 +220,14 @@ export class AIMessage extends BaseMessage {
 }
 
 export function isAIMessage(x: BaseMessage | null | undefined): x is AIMessage {
-  if (x == null) return false;
+  if (!x) return false;
   return x._getType() === "ai";
 }
 
 export function isAIMessageChunk(
   x: BaseMessageChunk | null | undefined
 ): x is AIMessageChunk {
-  if (x == null) return false;
+  if (!x) return false;
   return x._getType() === "ai";
 }
 
diff --git a/langchain-core/src/messages/base.ts b/langchain-core/src/messages/base.ts
index 679e9e847178..86468d47e926 100644
--- a/langchain-core/src/messages/base.ts
+++ b/langchain-core/src/messages/base.ts
@@ -546,7 +546,7 @@ export type BaseMessageLike =
 export function isBaseMessage(
   messageLike: unknown | null | undefined
 ): messageLike is BaseMessage {
-  if (messageLike == null) return false;
+  if (!messageLike) return false;
   return typeof (messageLike as BaseMessage)?._getType === "function";
 }
 
diff --git a/langchain-core/src/messages/chat.ts b/langchain-core/src/messages/chat.ts
index 634c7ec0784d..49b52521d867 100644
--- a/langchain-core/src/messages/chat.ts
+++ b/langchain-core/src/messages/chat.ts
@@ -48,7 +48,7 @@ export class ChatMessage
   static isInstance(
     message: BaseMessage | null | undefined
   ): message is ChatMessage {
-    if (message == null) return false;
+    if (!message) return false;
     return message._getType() === "generic";
   }
 
@@ -115,13 +115,13 @@ export class ChatMessageChunk extends BaseMessageChunk {
 export function isChatMessage(
   x: BaseMessage | null | undefined
 ): x is ChatMessage {
-  if (x == null) return false;
+  if (!x) return false;
   return x._getType() === "generic";
 }
 
 export function isChatMessageChunk(
   x: BaseMessageChunk | null | undefined
 ): x is ChatMessageChunk {
-  if (x == null) return false;
+  if (!x) return false;
   return x._getType() === "generic";
 }
diff --git a/langchain-core/src/messages/function.ts b/langchain-core/src/messages/function.ts
index 7b6f6dacdf3d..09c1a6bf7fa4 100644
--- a/langchain-core/src/messages/function.ts
+++ b/langchain-core/src/messages/function.ts
@@ -77,13 +77,13 @@ export class FunctionMessageChunk extends BaseMessageChunk {
 export function isFunctionMessage(
   x: BaseMessage | null | undefined
 ): x is FunctionMessage {
-  if (x == null) return false;
+  if (!x) return false;
   return x._getType() === "function";
 }
 
 export function isFunctionMessageChunk(
   x: BaseMessageChunk | null | undefined
 ): x is FunctionMessageChunk {
-  if (x == null) return false;
+  if (!x) return false;
   return x._getType() === "function";
 }
diff --git a/langchain-core/src/messages/human.ts b/langchain-core/src/messages/human.ts
index a58e41fa1b3c..a87a87d4551d 100644
--- a/langchain-core/src/messages/human.ts
+++ b/langchain-core/src/messages/human.ts
@@ -79,13 +79,13 @@ export class HumanMessageChunk extends BaseMessageChunk {
 export function isHumanMessage(
   x: BaseMessage | null | undefined
 ): x is HumanMessage {
-  if (x == null) return false;
+  if (!x) return false;
   return x.getType() === "human";
 }
 
 export function isHumanMessageChunk(
   x: BaseMessageChunk | null | undefined
 ): x is HumanMessageChunk {
-  if (x == null) return false;
+  if (!x) return false;
   return x.getType() === "human";
 }
diff --git a/langchain-core/src/messages/system.ts b/langchain-core/src/messages/system.ts
index 6f8337137ce9..9faed2e942eb 100644
--- a/langchain-core/src/messages/system.ts
+++ b/langchain-core/src/messages/system.ts
@@ -78,13 +78,13 @@ export class SystemMessageChunk extends BaseMessageChunk {
 export function isSystemMessage(
   x: BaseMessage | null | undefined
 ): x is SystemMessage {
-  if (x == null) return false;
+  if (!x) return false;
   return x._getType() === "system";
 }
 
 export function isSystemMessageChunk(
   x: BaseMessageChunk | null | undefined
 ): x is SystemMessageChunk {
-  if (x == null) return false;
+  if (!x) return false;
   return x._getType() === "system";
 }
diff --git a/langchain-core/src/messages/tool.ts b/langchain-core/src/messages/tool.ts
index a199a3cb2816..a02dc80d618c 100644
--- a/langchain-core/src/messages/tool.ts
+++ b/langchain-core/src/messages/tool.ts
@@ -118,7 +118,7 @@ export class ToolMessage extends BaseMessage implements DirectToolOutput {
   static isInstance(
     message: BaseMessage | null | undefined
   ): message is ToolMessage {
-    if (message == null) return false;
+    if (!message) return false;
     return message._getType() === "tool";
   }