fix: handle Gemini responses without candidates

[marandaneto]

💡 Motivation and Context

Fixes the issue reported in #418 where Gemini usage extraction can crash when the API response has a falsy candidates attribute, such as None. In that case, extract_gemini_web_search_count attempted to iterate over a non-iterable value while checking for grounding/web search metadata.

💚 How did you test it?

• uv run pytest posthog/test/ai/gemini/test_gemini.py -q
• uv run pytest posthog/test/ai/gemini/test_gemini.py::test_falsy_candidates_no_web_search -q
• uv run ruff check posthog/ai/gemini/gemini_converter.py posthog/test/ai/gemini/test_gemini.py

📝 Checklist

• I reviewed the submitted code.
• I added tests to verify the changes.
• I updated the docs if needed.
• No breaking change or entry added to the changelog.

If releasing new changes

• Ran sampo add to generate a changeset file

[greptile-apps]

Prompt To Fix All With AI

Fix the following 2 code review issues. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 2
posthog/test/ai/gemini/test_gemini.py:1173-1176
The team's convention is to prefer parameterised tests. The new test covers a single input (`candidates=None`), but the same fixed code path also handles an empty list (`[]`). Parameterising over both falsy values would give stronger regression coverage with no extra boilerplate.

```suggestion
@pytest.mark.parametrize("candidates_value", [None, []])
def test_falsy_candidates_no_web_search(mock_client, mock_google_genai_client, candidates_value):
    """Test that response with falsy candidates does not crash web search extraction."""

    mock_response = MagicMock()
```

### Issue 2 of 2
posthog/test/ai/gemini/test_gemini.py:1186-1187
If the test is parameterised, the `candidates` assignment needs to reference the parameter variable rather than the literal `None`.

```suggestion
    # candidates attribute exists but is falsy
    mock_response.candidates = candidates_value
```

_{Reviews (1): Last reviewed commit: "fix: handle Gemini responses without can..." | Re-trigger Greptile}

[github-actions]

posthog-python Compliance Report

Date: 2026-05-20 12:25:35 UTC
Duration: 4674964ms

⚠️ Some Tests Failed

29/45 tests passed, 16 failed

---

Capture Tests

✅ 29/29 tests passed

View Details

Test	Status	Duration
Format Validation.Event Has Required Fields	✅	516ms
Format Validation.Event Has Uuid	✅	1507ms
Format Validation.Event Has Lib Properties	✅	1505ms
Format Validation.Distinct Id Is String	✅	1507ms
Format Validation.Token Is Present	✅	1505ms
Format Validation.Custom Properties Preserved	✅	1505ms
Format Validation.Event Has Timestamp	✅	1507ms
Retry Behavior.Retries On 503	✅	9517ms
Retry Behavior.Does Not Retry On 400	✅	3505ms
Retry Behavior.Does Not Retry On 401	✅	3507ms
Retry Behavior.Respects Retry After Header	✅	9514ms
Retry Behavior.Implements Backoff	✅	23529ms
Retry Behavior.Retries On 500	✅	7500ms
Retry Behavior.Retries On 502	✅	7516ms
Retry Behavior.Retries On 504	✅	7506ms
Retry Behavior.Max Retries Respected	✅	23534ms
Deduplication.Generates Unique Uuids	✅	1496ms
Deduplication.Preserves Uuid On Retry	✅	7514ms
Deduplication.Preserves Uuid And Timestamp On Retry	✅	14522ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	✅	7509ms
Deduplication.No Duplicate Events In Batch	✅	1503ms
Deduplication.Different Events Have Different Uuids	✅	1507ms
Compression.Sends Gzip When Enabled	✅	1507ms
Batch Format.Uses Proper Batch Structure	✅	1507ms
Batch Format.Flush With No Events Sends Nothing	✅	1005ms
Batch Format.Multiple Events Batched Together	✅	1506ms
Error Handling.Does Not Retry On 403	✅	3508ms
Error Handling.Does Not Retry On 413	✅	3509ms
Error Handling.Retries On 408	✅	7509ms

Feature_Flags Tests

⚠️ 0/16 tests passed, 16 failed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	❌	509ms
Request Payload.Flags Request Uses V2 Query Param	❌	300851ms
Request Payload.Flags Request Hits Flags Path Not Decide	❌	301064ms
Request Payload.Flags Request Omits Authorization Header	❌	301015ms
Request Payload.Token In Flags Body Matches Init	❌	300981ms
Request Payload.Groups Round Trip	❌	301019ms
Request Payload.Groups Default To Empty Object	❌	300905ms
Request Payload.Person Properties Distinct Id Auto Populated When Caller Omits It	❌	301047ms
Request Payload.Disable Geoip False Propagates As Geoip Disable False	❌	300975ms
Request Payload.Disable Geoip Omitted Defaults To False	❌	300996ms
Request Payload.Flag Keys To Evaluate Contains Only Requested Key	❌	301035ms
Request Lifecycle.No Flags Request On Init Alone	❌	300943ms
Request Lifecycle.No Flags Request On Normal Capture	❌	301029ms
Request Lifecycle.Two Flag Calls Produce Two Remote Requests	❌	301029ms
Request Lifecycle.Mock Response Value Is Returned To Caller	❌	301030ms
Side Effect Events.Get Feature Flag Captures Feature Flag Called Event	❌	301007ms

Failures

request_payload.request_with_person_properties_device_id

Field 'token' not found in /flags request body at path 'token'. Available keys: ['distinct_id', 'groups', 'person_properties', 'group_properties', 'geoip_disable', 'device_id', 'flag_keys_to_evaluate', 'sentAt', 'api_key']

request_payload.flags_request_uses_v2_query_param

No error message

request_payload.flags_request_hits_flags_path_not_decide

No error message

request_payload.flags_request_omits_authorization_header

No error message

request_payload.token_in_flags_body_matches_init

No error message

request_payload.groups_round_trip

No error message

request_payload.groups_default_to_empty_object

No error message

request_payload.person_properties_distinct_id_auto_populated_when_caller_omits_it

No error message

request_payload.disable_geoip_false_propagates_as_geoip_disable_false

No error message

request_payload.disable_geoip_omitted_defaults_to_false

No error message

request_payload.flag_keys_to_evaluate_contains_only_requested_key

No error message

request_lifecycle.no_flags_request_on_init_alone

No error message

request_lifecycle.no_flags_request_on_normal_capture

No error message

request_lifecycle.two_flag_calls_produce_two_remote_requests

No error message

request_lifecycle.mock_response_value_is_returned_to_caller

No error message

side_effect_events.get_feature_flag_captures_feature_flag_called_event

No error message