From 437fe6d2164e80699a1520f229d610c4308f8269 Mon Sep 17 00:00:00 2001
From: Vadym Barda <vadym@langchain.dev>
Date: Fri, 21 Feb 2025 11:53:15 -0500
Subject: [PATCH] core[patch]: return ToolMessage from tools when tool call ID
 is empty string (#29921)

---
 libs/core/langchain_core/tools/base.py   |  2 +-
 libs/core/tests/unit_tests/test_tools.py | 11 +++++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/libs/core/langchain_core/tools/base.py b/libs/core/langchain_core/tools/base.py
index ff62f3091d4..3d98b50dda7 100644
--- a/libs/core/langchain_core/tools/base.py
+++ b/libs/core/langchain_core/tools/base.py
@@ -960,7 +960,7 @@ def _format_output(
     name: str,
     status: str,
 ) -> Union[ToolOutputMixin, Any]:
-    if isinstance(content, ToolOutputMixin) or not tool_call_id:
+    if isinstance(content, ToolOutputMixin) or tool_call_id is None:
         return content
     if not _is_message_content_type(content):
         content = _stringify(content)
diff --git a/libs/core/tests/unit_tests/test_tools.py b/libs/core/tests/unit_tests/test_tools.py
index afe8c09113a..06c82946ebe 100644
--- a/libs/core/tests/unit_tests/test_tools.py
+++ b/libs/core/tests/unit_tests/test_tools.py
@@ -2457,3 +2457,14 @@ def test_simple_tool_args_schema_dict() -> None:
     assert tool.args == {
         "a": {"title": "A", "type": "integer"},
     }
+
+
+def test_empty_string_tool_call_id() -> None:
+    @tool
+    def foo(x: int) -> str:
+        """Foo."""
+        return "hi"
+
+    assert foo.invoke({"type": "tool_call", "args": {"x": 0}, "id": ""}) == ToolMessage(
+        content="hi", name="foo", tool_call_id=""
+    )