fix(core): Fix error on langgraph resume

packages/core/src/tracing/langgraph/index.ts

@@ -136,7 +136,7 @@ function instrumentCompiledGraphInvoke(
             const recordInputs = options.recordInputs;
             const recordOutputs = options.recordOutputs;
             const inputMessages =
-              args.length > 0 ? ((args[0] as { messages?: LangChainMessage[] }).messages ?? []) : [];
+              args.length > 0 ? ((args[0] as { messages?: LangChainMessage[] } | null)?.messages ?? []) : [];
 
             if (inputMessages && recordInputs) {
               const normalizedMessages = normalizeLangChainMessages(inputMessages);

packages/core/test/tracing/langgraph-invoke-null-input.test.ts

@@ -0,0 +1,85 @@
+import { describe, expect, it, vi } from 'vitest';
+import { instrumentLangGraph } from '../../src/tracing/langgraph';
+
+/**
+ * Creates a minimal mock StateGraph that simulates LangGraph's StateGraph.
+ * The compile() method returns a mock CompiledGraph with an invoke() method.
+ */
+function createMockStateGraph(invokeResult: unknown = { messages: [] }) {
+  return {
+    compile: (options?: Record<string, unknown>) => {
+      return {
+        invoke: vi.fn().mockResolvedValue(invokeResult),
+        name: options?.name ?? 'test_graph',
+        builder: {
+          nodes: {},
+        },
+      };
+    },
+  };
+}
+
+describe('LangGraph invoke with null input (resume scenario)', () => {
+  it('should not throw TypeError when invoke is called with null as first argument', async () => {
+    const stateGraph = createMockStateGraph();
+    instrumentLangGraph(stateGraph, { recordInputs: true, recordOutputs: true });
+
+    const compiled = stateGraph.compile({ name: 'resume_agent' });
+
+    // Simulates graph.invoke(null, config) which is the standard pattern
+    // for resuming a LangGraph graph after a human-in-the-loop interrupt.
+    // Previously this would throw: TypeError: Cannot read properties of null (reading 'messages')
+    await expect(
+      compiled.invoke(null, {
+        configurable: { thread_id: 'thread-123' },
+      }),
+    ).resolves.not.toThrow();
+  });
+
+  it('should not throw TypeError when invoke is called with undefined as first argument', async () => {
+    const stateGraph = createMockStateGraph();
+    instrumentLangGraph(stateGraph, { recordInputs: true, recordOutputs: true });
+
+    const compiled = stateGraph.compile({ name: 'resume_agent' });
+
+    await expect(
+      compiled.invoke(undefined, {
+        configurable: { thread_id: 'thread-123' },
+      }),
+    ).resolves.not.toThrow();
+  });
+
+  it('should not throw when invoke is called with no arguments', async () => {
+    const stateGraph = createMockStateGraph();
+    instrumentLangGraph(stateGraph, { recordInputs: true, recordOutputs: true });
+
+    const compiled = stateGraph.compile({ name: 'resume_agent' });
+
+    await expect(compiled.invoke()).resolves.not.toThrow();
+  });
+
+  it('should still work correctly with a normal messages input', async () => {
+    const mockResult = {
+      messages: [
+        { role: 'user', content: 'hello' },
+        { role: 'assistant', content: 'Hi there!' },
+      ],
+    };
+    const stateGraph = createMockStateGraph(mockResult);
+    instrumentLangGraph(stateGraph, { recordInputs: true, recordOutputs: true });
+
+    const compiled = stateGraph.compile({ name: 'chat_agent' });
+
+    const result = await compiled.invoke({ messages: [{ role: 'user', content: 'hello' }] });
+    expect(result).toEqual(mockResult);
+  });
+
+  it('should still work correctly with an empty object input', async () => {
+    const stateGraph = createMockStateGraph();
+    instrumentLangGraph(stateGraph, { recordInputs: true, recordOutputs: true });
+
+    const compiled = stateGraph.compile({ name: 'resume_agent' });
+
+    await expect(compiled.invoke({}, { configurable: { thread_id: 'thread-456' } })).resolves.not.toThrow();
+  });
+});