From 719a1311b66a95fc18ccd3d673459e7bd5eadbea Mon Sep 17 00:00:00 2001
From: Ninja <142054318+ninjamaster1337@users.noreply.github.com>
Date: Fri, 10 Nov 2023 19:37:47 -0600
Subject: [PATCH] Fix delta role error when using custom LLM (#3223)

* Fix delta role error when using custom LLM

This addresses a delta chunk issue that happens when you use a custom baseURL on the openai chat model. Some models like llama 2 on openrouter may have a empty delta and result in a undefined error.

Example error:
```
Cannot read properties of undefined (reading 'role')",
  "error.stack": "TypeError: Cannot read properties of undefined (reading 'role')\n    at _convertDeltaToMessageChunk (/home/ubuntu/node_modules/langchain/dist/chat_models/openai.cjs:72:24)\n    at ChatOpenAI._streamResponseChunks (/home/ubuntu/node_modules/langchain/dist/chat_models/openai.cjs:409:27)\n    at process.processTicksAndRejections (node:internal/process/task_queues:95:5)\n    at async ChatOpenAI._streamIterator (/home/ubuntu/node_modules/langchain/dist/chat_models/base.cjs:77:34)\n    at async RunnableSequence._streamIterator (/home/ubuntu/node_modules/langchain/dist/schema/runnable/base.cjs:780:30)\n    at async Object.pull (/home/ubuntu/node_modules/langchain/dist/util/stream.cjs:73:41)
```

on _convertDeltaToMessageChunk, openai works fine but when you start using models from openrouter or other baseURL llms, it doesnt take in account for empty deltas and assumes theres always a value.

I was able to test with a custom baseURL and normal openai that this works with no errors on streaming after this tweak.

* add default role

* add ? on chunk text for streaming delta

* Simpler fix

* Revert

---------

Co-authored-by: jacoblee93 <jacoblee93@gmail.com>
---
 langchain/src/chat_models/openai.ts | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/langchain/src/chat_models/openai.ts b/langchain/src/chat_models/openai.ts
index cbda733aea9..7e3f72c3e8f 100644
--- a/langchain/src/chat_models/openai.ts
+++ b/langchain/src/chat_models/openai.ts
@@ -449,6 +449,9 @@ export class ChatOpenAI<
       }
 
       const { delta } = choice;
+      if (!delta) {
+        continue;
+      }
       const chunk = _convertDeltaToMessageChunk(delta, defaultRole);
       defaultRole = delta.role ?? defaultRole;
       const newTokenIndices = {