TypeError when invoking nested step function by in stack reference

[DaveLo]

This is a Bug report (or question?)

Description

For bug reports:

• What went wrong?
  Trying to invoke a child machine from parent by a ref to logical id. I set the logical id using the id property as described in the docs.
• What did you expect should have happened?
  It should deploy
• What was the config you used?
  I've added a boilerplate example that has the same error to make reproduction as easy as possible

serverless.yml

service: sfn-test-case

frameworkVersion: '2'

provider:
  name: aws
  runtime: nodejs12.x
  lambdaHashingVersion: 20201221
  region: us-east-1
  stage: dev
  eventBridge:
    useCloudFormation: true

  package:
    individually: true
    patterns:
      - "!*.json"
      - "!*.md"

stepFunctions:
  stateMachines:
    goodbye:
      type: STANDARD
      name: someMachineName-dev
      id: goodbyeMachine
      definition:
        StartAt: ending
        States:
          ending:
            Type: Pass
            End: true
    hello:
      type: STANDARD
      definition:
        StartAt: invokeChild
        States:
          invokeChild:
            Type: Task
            End: true
            Resource: arn:aws:states:::states:startExecution
            StateMachineArn:
              Ref: goodbyeMachine

plugins:
  - serverless-step-functions

• What stacktrace or error message from your provider did you see?

StackTrace

TypeError: Cannot read property 'StateMachineArn.$' of undefined
      at getStepFunctionsPermissions (/Users/**/**/sfn-test-case/node_modules/serverless-step-functions/lib/deploy/stepFunctions/compileIamRole.js:268:43)
      at /Users/**/**/sfn-test-case/node_modules/serverless-step-functions/lib/deploy/stepFunctions/compileIamRole.js:441:16
      at arrayMap (/Users/**/**/sfn-test-case/node_modules/lodash/lodash.js:653:23)
      at map (/Users/**/**/sfn-test-case/node_modules/lodash/lodash.js:9622:14)
      at Function.flatMap (/Users/**/**/sfn-test-case/node_modules/lodash/lodash.js:9325:26)
      at ServerlessStepFunctions.getIamPermissions (/Users/**/**/sfn-test-case/node_modules/serverless-step-functions/lib/deploy/stepFunctions/compileIamRole.js:401:12)
      at /Users/**/**/sfn-test-case/node_modules/serverless-step-functions/lib/deploy/stepFunctions/compileIamRole.js:504:56
      at Array.forEach (<anonymous>)
      at ServerlessStepFunctions.compileIamRole (/Users/**/**/sfn-test-case/node_modules/serverless-step-functions/lib/deploy/stepFunctions/compileIamRole.js:493:32)
      at ServerlessStepFunctions.tryCatcher (/Users/**/**/sfn-test-case/node_modules/bluebird/js/release/util.js:16:23)
      at Promise._settlePromiseFromHandler (/Users/**/**/sfn-test-case/node_modules/bluebird/js/release/promise.js:547:31)
      at Promise._settlePromise (/Users/**/**/sfn-test-case/node_modules/bluebird/js/release/promise.js:604:18)
      at Promise._settlePromiseCtx (/Users/**/**/sfn-test-case/node_modules/bluebird/js/release/promise.js:641:10)
      at _drainQueueStep (/Users/**/**/sfn-test-case/node_modules/bluebird/js/release/async.js:97:12)
      at _drainQueue (/Users/**/**/sfn-test-case/node_modules/bluebird/js/release/async.js:86:9)
      at Async._drainQueues (/Users/**/**/sfn-test-case/node_modules/bluebird/js/release/async.js:102:5)
      at Immediate.Async.drainQueues [as _onImmediate] (/Users/**/**/sfn-test-case/node_modules/bluebird/js/release/async.js:15:14)
      at processImmediate (node:internal/timers:464:21)

Additional Data

• Serverless Framework Core Version you're using:

Operating System:          darwin
     Node Version:              16.4.0
     Framework Version:         2.66.0 (local)
     Plugin Version:            5.5.1
     SDK Version:               4.3.0
     Components Version:        3.17.2

• The Plugin Version you're using: 3.2.0

[TimDN]

Just adding my two cents as i've also been trying to get this working. Based on this page should not StateMachineArn be specified in a Parameters object ? https://docs.aws.amazon.com/step-functions/latest/dg/sample-start-workflow.html

This is what i've been using to try to get this working.

serverless.yml

stepFunctions:
  validate: true
  stateMachines:
    testMachine:
      name: testMachine
      id: TestMachine
      definition:
        StartAt: Test
        States:
          Test:
            Type: Pass
            End: true
    testNested:
      name: nestedTest
      definition:
        StartAt: Test
        States: 
          Test:
            Type: Task
            Resource: arn:aws:states:::states:startExecution.sync:2
            Parameters:
              StatMachineArn:
                Fn::GetAtt: [TestMachine, Arn]
            End: True

However using that format results in another error where the referenced state machine resource is set to null in the generated role. Leading to the error
The CloudFormation template is invalid: [/Resources/NestedTestRole/Type/Policies/0/PolicyDocument/Statement/0/Resource/0] 'null' values are not allowed in templates
I've tried some different ways to reference the state machine but even when using a hardcoded ARN results in the same error.

This is the generated role

cloudformation-template-update-stack.json

{
"NestedTestRole": {
      "Type": "AWS::IAM::Role",
      "Properties": {
        "AssumeRolePolicyDocument": {
          "Version": "2012-10-17",
          "Statement": [
            {
              "Effect": "Allow",
              "Principal": {
                "Service": {
                  "Fn::Sub": "states.${AWS::Region}.amazonaws.com"
                }
              },
              "Action": "sts:AssumeRole"
            }
          ]
        },
        "Policies": [
          {
            "PolicyName": "REMOVED THIS",
            "PolicyDocument": {
              "Version": "2012-10-17",
              "Statement": [
                {
                  "Effect": "Allow",
                  "Action": [
                    "states:StartExecution"
                  ],
                  "Resource": [
                    null
                  ]
                },
                {
                  "Effect": "Allow",
                  "Action": [
                    "states:DescribeExecution",
                    "states:StopExecution"
                  ],
                  "Resource": "*"
                },
                {
                  "Effect": "Allow",
                  "Action": [
                    "events:PutTargets",
                    "events:PutRule",
                    "events:DescribeRule"
                  ],
                  "Resource": [
                    {
                      "Fn::Sub": [
                        "arn:${AWS::Partition}:events:${AWS::Region}:${AWS::AccountId}:rule/StepFunctionsGetEventsForStepFunctionsExecutionRule",
                        {}
                      ]
                    }
                  ]
                }
              ]
            }
          }
        ]
      }
    }
}