custom-resources: can't flatten response containing null property value

[pahud]

This function will fail if the response property contains the null value.

aws-cdk/packages/@aws-cdk/custom-resources/lib/aws-custom-resource/runtime/index.ts

Lines 11 to 23 in e95b52e

	function flatten(object: object): { [key: string]: string } {
	return Object.assign(
	{},
	...function _flatten(child: any, path: string[] = []): any {
	return [].concat(...Object.keys(child)
	.map(key =>
	typeof child[key] === 'object'
	? _flatten(child[key], path.concat([key]))
	: ({ [path.concat([key]).join('.')]: child[key] })
	));
	}(object)
	);
	}

Reproduction Steps

const clusterInfo = new cr.AwsCustomResource(stack, 'clusterInfo', {
  onUpdate: {
    service: 'EKS',
    action: 'describeCluster',
    region,
    parameters: {
      name: cluster.clusterName,
    },
    physicalResourceId: cluster.clusterName,
  },
})

Will get response like this

 { name: 'cluster-a5bc1663-3159-4112-9c28-e8c84e730606',
     arn:
      'arn:aws:eks:ap-northeast-1:903779448426:cluster/cluster-a5bc1663-3159-4112-9c28-e8c84e730606',
     createdAt: 2019-11-15T01:28:24.825Z,
     version: '1.14',
     endpoint: '...',
     roleArn: '...',
     resourcesVpcConfig:
      { subnetIds: [Array],
        securityGroupIds: [Array],
        vpcId: 'vpc-497a492d',
        endpointPublicAccess: true,
        endpointPrivateAccess: false },
     logging: { clusterLogging: [Array] },
     status: 'ACTIVE',
     certificateAuthority:
      { data: '...' },
     clientRequestToken: null,
     platformVersion: 'eks.2' } }

And the clientRequestToken would be null, which breaks the flatten() function.

A simple additional check like this can fix this issue but I'm not sure if it's a good way to fix it.

function flatten(object) {
    return Object.assign({}, ...function _flatten(child, path = []) {
        return [].concat(...Object.keys(child)
            .map(key => typeof child[key] === 'object' && child[key] != null
            ? _flatten(child[key], path.concat([key]))
            : ({ [path.concat([key]).join('.')]: child[key] })));
    }(object));
}

Error Log

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