fix(Anthropic): Handle empty tool input (#960)

* fix(Anthropic): Handle empty tool input

* Fix linting errors

---------

Co-authored-by: Sergio Bayona <[email protected]>
Co-authored-by: Andrei Bondarev <[email protected]>

Author: 3 people

lib/langchain/llm/anthropic.rb

@@ -177,7 +177,7 @@ def tool_calls_from_choice_chunks(chunks)
           "id" => first_block.dig("content_block", "id"),
           "type" => "tool_use",
           "name" => first_block.dig("content_block", "name"),
-          "input" => JSON.parse(input).transform_keys(&:to_sym)
+          "input" => input.empty? ? nil : JSON.parse(input).transform_keys(&:to_sym)
         }
       end.compact
     end

spec/fixtures/llm/anthropic/chat_stream_with_empty_tool_input.json

@@ -0,0 +1,11 @@
+[
+    {"type": "message_start", "message": {"id": "msg_014p7gG3wDgGV9EUtLvnow3U", "type": "message", "role": "assistant", "model": "claude-3-haiku-20240307", "content": [], "stop_reason": null}},
+    {"type": "content_block_start", "index": 0, "content_block": {"type": "text", "text": ""}},
+    {"type": "content_block_delta", "index": 0, "delta": {"type": "text_delta", "text": "I'll check the weather for you:"}},
+    {"type": "content_block_stop", "index": 0},
+    {"type": "content_block_start", "index": 1, "content_block": {"type": "tool_use", "id": "toolu_01T1x1fJ34qAmk2tNTrN7Up6", "name": "get_weather", "input": {}}},
+    {"type": "content_block_delta", "index": 1, "delta": {"type": "input_json_delta", "partial_json": ""}},
+    {"type": "content_block_stop", "index": 1},
+    {"type": "message_delta", "delta": {"stop_reason": "tool_use", "stop_sequence": null}, "usage": {"output_tokens": 10}},
+    {"type": "message_stop"}
+  ]

spec/langchain/llm/anthropic_spec.rb

@@ -175,6 +175,23 @@
         expect(rsp.tool_calls.first["name"]).to eq("get_weather")
         expect(rsp.tool_calls.first["input"]).to eq({location: "San Francisco, CA", unit: "fahrenheit"})
       end
+
+      context "response has empty input" do
+        let(:fixture) { File.read("spec/fixtures/llm/anthropic/chat_stream_with_empty_tool_input.json") }
+
+        it "handles empty input in tool calls correctly" do
+          # The test will pass if no exception is raised during processing
+          rsp = subject.chat(messages: [{role: "user", content: "What's the weather?"}], &stream_handler)
+
+          # Verify the response
+          expect(rsp).to be_a(Langchain::LLM::AnthropicResponse)
+          expect(rsp.chat_completion).to eq("I'll check the weather for you:")
+
+          # Verify the tool call with empty input is handled correctly
+          expect(rsp.tool_calls.first["name"]).to eq("get_weather")
+          expect(rsp.tool_calls.first["input"]).to be_nil  # Should be nil (null in Ruby) because input was empty
+        end
+      end
     end
   end
 end