From 7a5e1bcf99ab445cf9438f5412f19e5024e5e123 Mon Sep 17 00:00:00 2001
From: Michael Reed <1062477+haywood@users.noreply.github.com>
Date: Mon, 20 May 2024 18:06:27 -0400
Subject: [PATCH] core[patch]: Fix NPE in
 function_calling._get_python_function_required_args (#21863)

Example error message:
line 206, in _get_python_function_required_args
    if is_function_type and required[0] == "self":
                            ~~~~~~~~^^^
IndexError: list index out of range

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---------

Co-authored-by: Bagatur <baskaryan@gmail.com>
---
 libs/core/langchain_core/utils/function_calling.py     |  4 ++--
 .../tests/unit_tests/utils/test_function_calling.py    | 10 ++++++++++
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/libs/core/langchain_core/utils/function_calling.py b/libs/core/langchain_core/utils/function_calling.py
index ead26d66aa8..932b329f870 100644
--- a/libs/core/langchain_core/utils/function_calling.py
+++ b/libs/core/langchain_core/utils/function_calling.py
@@ -203,9 +203,9 @@ def _get_python_function_required_args(function: Callable) -> List[str]:
 
     is_function_type = isinstance(function, FunctionType)
     is_method_type = isinstance(function, MethodType)
-    if is_function_type and required[0] == "self":
+    if required and is_function_type and required[0] == "self":
         required = required[1:]
-    elif is_method_type and required[0] == "cls":
+    elif required and is_method_type and required[0] == "cls":
         required = required[1:]
     return required
 
diff --git a/libs/core/tests/unit_tests/utils/test_function_calling.py b/libs/core/tests/unit_tests/utils/test_function_calling.py
index 1f818fe6bae..9973d972208 100644
--- a/libs/core/tests/unit_tests/utils/test_function_calling.py
+++ b/libs/core/tests/unit_tests/utils/test_function_calling.py
@@ -146,6 +146,16 @@ def test_function_optional_param() -> None:
     assert set(req) == {"b"}
 
 
+def test_function_no_params() -> None:
+    def nullary_function() -> None:
+        """nullary function"""
+        pass
+
+    func = convert_to_openai_function(nullary_function)
+    req = func["parameters"]["required"]
+    assert not req
+
+
 class FakeCall(BaseModel):
     data: str