fix: 'NoneType' object is not iterable

[ananthanarayanan-28]

Link to Issue or Description of Change

1. Link to an existing issue (if applicable):

• Closes: TypeError: 'NoneType' object is not iterable #3987
• Related: Background execution error: 'NoneType' object has no attribute 'update_timestamp_tz' #3596

2. Or, if no issue exists, describe the change:

Problem:
Idea about my use case
I'm building the report generation system using google-ask (1.18.0) and building multiple subagents here, I'm passing the one subagent Agent as a tool to another Parent Agent. Note: Sub-agent can do web search.
here, parent agent triggers multiple sub-agent (same agent) multiple times according to use case or complexity of the user input

Describe the bug
here, the bug sometimes sub agents doesn't provide the proper output and resulted in the

merged_text = '\n'.join(p.text for p in last_content.parts if p.text)
^^^^^^^^^^^^^^^^^^
TypeError: 'NoneType' object is not iterable
and it's breaking the system of Agents workflow

Solution:
Creating fallback if there is no last_content.parts it will return the empty parts so we won't face the NoneType issue

Testing Plan

Created a unit test file for this issue
test_google_search_agent_tool_repro.py

Unit Tests:

• I have added or updated unit tests for my change.
• All unit tests pass locally.

Please include a summary of passed pytest results.
3677 passed, 2208 warnings in 42.64s

Manual End-to-End (E2E) Tests:
N/A

Checklist

• I have read the CONTRIBUTING.md document.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• I have manually tested my changes end-to-end.
• Any dependent changes have been merged and published in downstream modules.

Additional context

N/A

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[gemini-code-assist]

Summary of Changes

Hello @ananthanarayanan-28, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request resolves a critical TypeError that could arise in agent tools when processing responses where the last_content.parts attribute was unexpectedly None. The change implements a more resilient handling of potentially null content parts, ensuring that the system gracefully processes such cases instead of crashing. This significantly improves the stability of agent workflows, particularly when sub-agents might return incomplete or malformed outputs.

Highlights

• Bug Fix: Addresses a TypeError: 'NoneType' object is not iterable that occurred when last_content.parts was None in agent tool responses, preventing agent workflow failures.
• Robustness Improvement: Introduces a fallback mechanism to ensure last_content.parts is treated as an empty iterable if it's None, and safely extracts text attributes using getattr.
• New Unit Test: Adds a dedicated unit test (test_google_search_agent_tool_repro.py) to specifically reproduce and verify the fix for the NoneType issue.

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[gemini-code-assist]

Code Review

This pull request fixes a TypeError that occurs when last_content.parts is None. The fix involves checking for None and providing an empty list as a fallback. A unit test is also added to verify the fix.

My review focuses on simplifying the implementation. The current change, while effective, introduces unnecessary complexity and a subtle change in behavior regarding the handling of empty strings. I've suggested a more concise and readable implementation that preserves the original logic while still fixing the bug. The changes are duplicated across two files, and my feedback applies to both.

[ryanaiagent]

Hi @ananthanarayanan-28, Thank you for your contribution! We appreciate you taking the time to submit this pull request.
Can you please fix the lint errors using autoformat.sh. Let us know once you finish so that we can proceed with the review.

[ananthanarayanan-28]

@ryanaiagent can you check now, done with lint errors

[gemini-code-assist]

Code Review

This pull request effectively addresses a TypeError that occurs when last_content.parts is None. The fix, which provides an empty list as a fallback, is correct and has been applied to both AgentTool and GoogleSearchAgentTool. A new unit test has been added to verify this fix, which is great. I've made a couple of suggestions to make the code slightly more concise by inlining the fallback logic. Overall, this is a good fix.

[ananthanarayanan-28]

@ryanaiagent @adk-bot any updates on this PR?

[ananthanarayanan-28]

/gemini review.

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[ananthanarayanan-28]

/gemini review.

[gemini-code-assist]

Code Review

This pull request correctly fixes a TypeError that occurs when last_content.parts is None by providing an empty list as a fallback. The fix is applied in both AgentTool and GoogleSearchAgentTool, and a new unit test is added to verify this behavior, which is great. My review includes feedback on a potential resource leak and significant code duplication in GoogleSearchAgentTool, with suggestions for improvement.

[gemini-code-assist]

I noticed that this run_async method is missing a call to await runner.close() after the async with Aclosing(...) block (around line 125).

The parent class AgentTool includes this call, and a comment there highlights its importance for resource cleanup:

# Clean up runner resources (especially MCP sessions)
# to avoid "Attempted to exit cancel scope in a different task" errors
await runner.close()

The absence of this call could lead to resource leaks. Please add await runner.close() before the if not last_content: check.

[gemini-code-assist]

This run_async method is almost a complete copy of AgentTool.run_async. This code duplication makes the code harder to maintain, as bugs (like the one this PR fixes) need to be fixed in multiple places.

Since you are already modifying this code, it would be a great opportunity to refactor and reduce duplication. One approach could be to make AgentTool.run_async more extensible so that this method can call super().run_async() and then just add its specific logic for grounding_metadata.