Repository navigation
CognitoEventUserPoolsPreTokenGenV2 deserialization error when groupConfiguration is null #1129
Description
Cognito's pre-token v2 hook can sometimes receive a null groupConfiguration field value. The cognito documentation includes example JSON rather than schema, so it's not clear whether this is a cognito bug or not. But it definitely happens at runtime for some user pools.
In any case, the rust structure fails to deserialize the event with
PreTokenGenerationV2_0 failed with error failed to deserialize the incoming data into the function's payload type: [request.groupConfiguration] request.groupConfiguration: invalid type: null, expected struct GroupConfiguration at line 1 column 835
In any case, the obvious backwards-compatible fix is to add #[serde(default)] to the field. Looks like maybe that was the intent and it just got missed on that field? Happy to test the fix / send a PR.
Activity
jlizen commentedon Mar 17, 2026
Adding the default is good, thanks!
fix handling of null groupConfiguration
jct-tympanon commentedon Mar 18, 2026
PR sent. i had to do a little more than "serde(default)", but it follows the pattern of other fields nearby. i verified the patch in my own cognito app (with a V2 pre-token trigger).
consolidate nullish deserializers.
fix handling of null groupConfiguration (#1130)
github-actions commentedon Mar 19, 2026
This issue is now closed. Comments on closed issues are hard for our team to see.
If you need more assistance, please either tag a team member or open a new issue that references this one.
jlizen commentedon Mar 19, 2026
Fix has been released:
https://crates.io/crates/aws_lambda_events/1.1.2