aws-events: Support 'null' values for event matching

[homanchou]

I'm trying to use AWS CDK to create an eventbridge rule.

The custom event will have a detail payload where I only want to match on events where order_item_id is null.

Here is the rule in cdk:

rule.addEventPattern({
  account: ['xxxxxxxxx'],
  detailType: ['inventory_adjusted'],
  detail: {
    'order_item_id': [null]
  }
})

And according to aws documentation, this is allowed:

https://docs.aws.amazon.com/AmazonCloudWatch/latest/events/CloudWatchEventsandEventPatterns.html

To match events where the value of responseElements is null, use the following pattern, which would match the event example.
{ "detail": { "responseElements": [null] } }

However, when deploying with cdk I get this error:

development failed: ValidationError: [/Resources/sendinventoryadjustmentstolambda8954C2E5/Type/EventPattern/detail/order_item_id/0] 'null' values are not allowed in templates >[/Resources/sendinventoryadjustmentstolambda8954C2E5/Type/EventPattern/detail/order_item_id/0] 'null' values are not allowed in templates

And here is the cdk synth for the area around the rule:

EventPattern:
    account:
      - "xxxxxxxxx"
    detail-type:
      - inventory_adjusted
    detail:
      order_item_id:
        - null

Indeed it is null... which apparently isn't allowed in yaml template, but then how do I express this in CDK?

Reproduction Steps

create a rule that tries to match a null value for detail key

rule.addEventPattern({
  account: ['xxxxxxxxx'],
  detailType: ['inventory_adjusted'],
  detail: {
    'order_item_id': [null]
  }
})

Error Log

development failed: ValidationError: [/Resources/sendinventoryadjustmentstolambda8954C2E5/Type/EventPattern/detail/order_item_id/0] 'null' values are not allowed in templates >[/Resources/sendinventoryadjustmentstolambda8954C2E5/Type/EventPattern/detail/order_item_id/0] 'null' values are not allowed in templates

Environment

• **CLI Version :

cdk --version
1.45.0 (build 0cfab15)

• Framework Version:
• **Node.js Version:

node -v
v11.15.0

• **OS : osX 10.14.6
• **Language (Version): typescript

Other

---

This is 🐛 Bug Report

[rix0rrr]

Good question. There's a good chance you can't. Looks like CloudFormation doesn't allow it, so the only way to make patterns like this is by using the API directly.

A custom resource would be the way to go.