When a subscription is created using cloudformation:
```
"ProfileChangedSubscription": {
      "Type": "AWS::SNS::Subscription",
      "Properties": {
        "Endpoint": {
          "Fn::GetAtt": [
            "ProfileChangedQueue",
            "Arn"
          ]
        },
        "Protocol": "sqs",
        "FilterPolicy": {
          "eventType": [
            "created"
          ]
        },
        "TopicArn": {
          "Fn::ImportValue": {
            "Fn::Sub": "${ProfilesProfilePublishStack}-ProfileChangedTopic"
          }
        }
      }
    }
```

The specified subscription filter policy is not created. When I run `get-subscription-attributes`, I get information about non-existing filter policy:

```
{
    "Attributes": {
        "TopicArn": "arn:aws:sns:us-east-1:000000000000:profile-changed-topic",
        "Endpoint": "arn:aws:sqs:us-east-1:000000000000:profile-changed-queue",
        "Protocol": "sqs",
        "SubscriptionArn": "arn:aws:sns:us-east-1:000000000000:profile-changed-topic:936a58be-525b-4228-bfdb-c4b2f6048e8c",
        "FilterPolicy": "None"
    }
}
```
LOG.debug('Extract resource attribute: %s %s' % (resource_type, attribute))
    
    if resource_type == 'Lambda::Function':
        actual_attribute = 'FunctionArn' if attribute == 'Arn' else attribute
        return resource['Configuration'][actual_attribute]
    elif resource_type == 'DynamoDB::Table':
        actual_attribute = 'LatestStreamArn' if attribute == 'StreamArn' else attribute
        value = resource['Table'].get(actual_attribute)
        return value
    elif resource_type == 'ApiGateway::RestApi':
        if attribute == 'PhysicalResourceId':
            return resource['id']
        if attribute == 'RootResourceId':
            resources = aws_stack.connect_to_service('apigateway').get_resources(restApiId=resource['id'])['items']
            for res in resources:
                if res['path'] == '/' and not res.get('parentId'):
                    return res['id']
    elif resource_type == 'ApiGateway::Resource':
        if attribute == 'PhysicalResourceId':
            return resource['id']
    return resource.get(attribute)
def resolve_ref(stack_name, ref, resources, attribute):