Bug: SnsSchema parsing fails when `Subject` is null

[nied]

Expected Behavior

Sns events with a Subject that is null should pass schema parsing with SnsSchema.

Current Behavior

For an event like this:

{
  "Records": [
    {
      "EventSource": "aws:sns",
      "EventVersion": "1.0",
      "EventSubscriptionArn": "a subscription arn",
      "Sns": {
        "Type": "Notification",
        "MessageId": "a message id",
        "TopicArn": "an arn",
        "Subject": null,
        "Message": "hi there",
        "Timestamp": "2024-12-04T08:00:04.497Z",
        "SignatureVersion": "1",
        "Signature": "",
        "SigningCertUrl": "http://www.google.com",
        "UnsubscribeUrl": "http://www.google.com",
        "MessageAttributes": {}
      }
    }
  ]
}

The following fails:

import { SnsSchema } from '@aws-lambda-powertools/parser/schemas';

SnsSchema.parse(event)

This is due to Subject being null. It can be omitted or undefined, but in the case of null it seems to throw. However, it is a valid case for SNS to have Subject be null.

Code snippet

import { SnsSchema } from '@aws-lambda-powertools/parser/schemas';

SnsSchema.parse(
{
  "Records": [
    {
      "EventSource": "aws:sns",
      "EventVersion": "1.0",
      "EventSubscriptionArn": "a subscription arn",
      "Sns": {
        "Type": "Notification",
        "MessageId": "a message id",
        "TopicArn": "an arn",
        "Subject": null,
        "Message": "hi there",
        "Timestamp": "2024-12-04T08:00:04.497Z",
        "SignatureVersion": "1",
        "Signature": "",
        "SigningCertUrl": "http://www.google.com",
        "UnsubscribeUrl": "http://www.google.com",
        "MessageAttributes": {}
      }
    }
  ]
}
)

Steps to Reproduce

Run the codesnippet above and it should fail

Possible Solution

Allow the Subject field to be null as well as omitted

Powertools for AWS Lambda (TypeScript) version

latest

AWS Lambda function runtime

22.x

Packaging format used

npm

Execution logs

[boring-cyborg]

Thanks for opening your first issue here! We'll come back to you as soon as we can.
In the meantime, check out the #typescript channel on our Powertools for AWS Lambda Discord: Invite link

[am29d]

Hey Nies, thanks for opening the issue! While the fix is easy, I will take a closer look why we missed it in our tests.

Feel free to drop a PR, if you like, since you have spotted it first 😁.

[codyfrisch]

@am29d I just came here because this started happening to me. I'm almost willing to posit that AWS actually changed it because @types/aws-lambda is Subject?: string as well. I have no proof of course, I worked around it by sending a subject.