fix(langchain): Prevent exception when using plan & execute agent wit…

…h no tools (#6744)

Co-authored-by: Brace Sproul <[email protected]>

langchain/src/experimental/plan_and_execute/agent_executor.ts

@@ -132,7 +132,7 @@ export class PlanAndExecuteAgentExecutor extends BaseChain {
   }) {
     let agent;
 
-    if (isDynamicStructuredTool(tools[0])) {
+    if (tools.length > 0 && isDynamicStructuredTool(tools[0])) {
       agent = StructuredChatAgent.fromLLMAndTools(llm, tools, {
         humanMessageTemplate,
         inputVariables: ["previous_steps", "current_step", "agent_scratchpad"],

langchain/src/experimental/plan_and_execute/tests/plan_and_execute.int.test.ts

@@ -67,3 +67,19 @@ test.skip("Run agent with a sequential math problem", async () => {
 
   // console.log(result);
 });
+
+test.skip("Should run agent with no tools", async () => {
+  const model = new ChatOpenAI({
+    temperature: 0,
+    modelName: "gpt-3.5-turbo",
+    verbose: true,
+  });
+  const executor = await PlanAndExecuteAgentExecutor.fromLLMAndTools({
+    llm: model,
+    tools: [],
+  });
+
+  await executor.call({
+    input: `Who is the current president of the United States? What is their current age raised to the second power?`,
+  });
+});