`Cannot read properties of undefined (reading 'some')` while generating a response

[SimonBaars]

Operating System

ArchLinux (though this is not OS dependent)

Environment (if applicable)

Node v22.18.0

Firebase SDK Version

12.1.0

Firebase SDK Product(s)

AI

Project Tooling

React app with webpack

Detailed Problem Description

When I have an AI agent, I get this error often after the agent has done a couple of tool calls:

Cannot read properties of undefined (reading 'some')
TypeError: Cannot read properties of undefined (reading 'some')
    at http://localhost:3000/static/js/bundle.js:194967:35
    at Array.forEach (<anonymous>)
    at mapGenerateContentCandidates (http://localhost:3000/static/js/bundle.js:194945:16)
    at mapGenerateContentResponse (http://localhost:3000/static/js/bundle.js:194906:47)
    at processGenerateContentResponse (http://localhost:3000/static/js/bundle.js:195242:12)
    at async generateContent (http://localhost:3000/static/js/bundle.js:195233:35)
    at async ChatSession.sendMessage (http://localhost:3000/static/js/bundle.js:195564:5)
    at async http://localhost:3000/static/js/bundle.js:7659:16
    at async http://localhost:3000/static/js/bundle.js:7726:7

The error seems to come from this line specifically:

firebase-js-sdk/packages/ai/src/googleai-mappers.ts

Line 179 in c5f08a9

candidate.content?.parts.some(

Basically, it appears that under certain conditions, the parts may be undefined. But it's unclear to me why.

Steps and code to reproduce issue

Here's my ChatWidget:

ChatWidget.js

Basically, if I do a query that evokes a tool response which fetches a large file which is then returned to the agent, this error occurs. Though it doesn't seem to be consistent always. I almost feel like I'm being rate-limited, but the error is pretty cryptic and I'm not sending that many tokens through the model.

[google-oss-bot]

I couldn't figure out how to label this issue, so I've labeled it for a human to triage. Hang tight.

[dlarocque]

Hi @SimonBaars thanks for reporting this issue! This is definitely a bug. In the SDK, we expect to always get back parts, but it seems there is a bug in the server that causes a response to contain no parts.

Since this error is cryptic, we could try to detect this case and throw a more helpful error, or try to handle this more gracefully.

[dlarocque]

This is a duplicate of #9125

[SimonBaars]

When I run into the bug and do the same behavior time after time again (unlike the author of the linked issue states), I can definitely consistently reproduce it. Let me check if I can distill it into a minimal script.

[dlarocque]

When I run into the bug and do the same behavior time after time again (unlike the author of the linked issue states), I can definitely consistently reproduce it. Let me check if I can distill it into a minimal script.

A script that reproduces this would be really helpful! if you create one please share it in the other issue i linked