diff --git a/lib/langchain/assistant.rb b/lib/langchain/assistant.rb
index 92ec49139..74772ac38 100644
--- a/lib/langchain/assistant.rb
+++ b/lib/langchain/assistant.rb
@@ -309,7 +309,7 @@ def handle_user_or_tool_message
     end
 
     def set_state_for(response:)
-      if response.tool_calls.any?
+      if response.tool_calls&.any?
         :in_progress
       elsif response.chat_completion
         :completed
diff --git a/lib/langchain/assistant/llm/adapters/openai.rb b/lib/langchain/assistant/llm/adapters/openai.rb
index 67b734bbb..8eac0ecfe 100644
--- a/lib/langchain/assistant/llm/adapters/openai.rb
+++ b/lib/langchain/assistant/llm/adapters/openai.rb
@@ -39,7 +39,8 @@ def build_chat_params(
           # @param tool_calls [Array] The tool calls
           # @param tool_call_id [String] The tool call ID
           # @return [Messages::OpenAIMessage] The OpenAI message
-          def build_message(role:, content: nil, image_url: nil, tool_calls: [], tool_call_id: nil)
+          def build_message(role:, content: nil, image_url: nil, tool_calls: nil, tool_call_id: nil)
+            tool_calls ||= []
             Messages::OpenAIMessage.new(role: role, content: content, image_url: image_url, tool_calls: tool_calls, tool_call_id: tool_call_id)
           end