I am trying to deploy a lambda using `serverless-localstack` plugin, but I get always the following error:

```
localstack_1  | 2019-12-19 15:30:43,891:API: 127.0.0.1 - - [19/Dec/2019 15:30:43] "PUT /serverless-deploy-bucket/serverless/myservice/dev/1576769443675-2019-12-19T15%3A30%3A43.675Z/compiled-cloudformation-template.json HTTP/1.1" 200 -
localstack_1  | 2019-12-19T15:30:43:DEBUG:localstack.services.cloudformation.cloudformation_listener: Error response from CloudFormation (400) POST /: b'<ErrorResponse xmlns="http://cloudformation.amazonaws.com/doc/2010-05-15/">\n  <Error>\n    <Type>Sender</Type>\n    <Code>ValidationError</Code>\n    <Message>Stack with id myservice-dev does not exist</Message>\n  </Error>\n  <RequestId>cf4c737e-5ae2-11e4-a7c9-ad44eEXAMPLE</RequestId>\n</ErrorResponse>'
localstack_1  | 2019-12-19T15:30:43:WARNING:localstack.services.awslambda.lambda_api: Function not found: arn:aws:lambda:us-east-1:000000000000:function:myservice-dev-mylambda
localstack_1  | 2019-12-19T15:30:44:ERROR:localstack.services.generic_proxy: Error forwarding request: 'str' object has no attribute 'get' Traceback (most recent call last):
localstack_1  |   File "/opt/code/localstack/localstack/services/generic_proxy.py", line 242, in forward
localstack_1  |     path=path, data=data, headers=forward_headers)
localstack_1  |   File "/opt/code/localstack/localstack/services/cloudformation/cloudformation_listener.py", line 159, in forward_request
localstack_1  |     modified_request = transform_template(req_data)
localstack_1  |   File "/opt/code/localstack/localstack/services/cloudformation/cloudformation_listener.py", line 83, in transform_template
localstack_1  |     if parsed.get('Transform') == 'AWS::Serverless-2016-10-31':
localstack_1  | AttributeError: 'str' object has no attribute 'get'

localstack_1  | 2019-12-19T15:30:45:ERROR:localstack.services.generic_proxy: Error forwarding request: 'str' object has no attribute 'get' Traceback (most recent call last):
localstack_1  |   File "/opt/code/localstack/localstack/services/generic_proxy.py", line 242, in forward
localstack_1  |     path=path, data=data, headers=forward_headers)
localstack_1  |   File "/opt/code/localstack/localstack/services/cloudformation/cloudformation_listener.py", line 159, in forward_request
localstack_1  |     modified_request = transform_template(req_data)
localstack_1  |   File "/opt/code/localstack/localstack/services/cloudformation/cloudformation_listener.py", line 83, in transform_template
localstack_1  |     if parsed.get('Transform') == 'AWS::Serverless-2016-10-31':
localstack_1  | AttributeError: 'str' object has no attribute 'get'

[...]
```

This is the launch command for `localstack` (no errors):

```
SERVICES="iam,s3,sns,lambda,sts,cloudformation" LAMBDA_REMOTE_DOCKER=false LAMBDA_DOCKER_NETWORK=host \
LAMBDA_EXECUTOR=docker DEBUG=1 localstack start --docker
```

This is the `serverless` configuration:
```
service: myservice

provider:
  name: aws
  runtime: nodejs10.x
  deploymentBucket:
    name: serverless-deploy-bucket
  environment:
    NODE_ENV: ${env:NODE_ENV}

plugins:
  - serverless-localstack

custom:
  localstack:
    debug: true
    host: http://localhost
    lambda:
      mountCode: true

functions:
  mylambda:
    handler: index.handler
    events:
        - sns: ${env:SNS_INPUT_TOPIC_ARN}
```

This is the deploy command for `serverless` (all needed S3 buckets and SNS topics are created before deploy):

```
NODE_ENV=local SNS_INPUT_TOPIC_ARN="arn:aws:sns:us-east-1:000000000000:mytopic" node node_modules/serverless/bin/serverless.js deploy --noTimeout
```

I've tried also to set `mountCode` to false in serverless configuration, but same result.

`os`: MacOS 10.15
`Docker`: 2.1.0.5
`Python`: 3.7.4
`localstack`: 0.10.6
`serverless`: 1.59.3
`serverless-localstack`: 0.4.22
response = run_safe(lambda: safe_requests.get(url, verify=False))
        if not response or response.status_code >= 400:
            
            if '://localhost' in url or re.match(r'.*s3(\-website)?\.([^\.]+\.)?amazonaws.com.*', url):
                parsed_path = urlparse.urlparse(url).path.lstrip('/')
                parts = parsed_path.partition('/')
                client = aws_stack.connect_to_service('s3')
                result = client.get_object(Bucket=parts[0], Key=parts[2])
                body = to_str(result['Body'].read())
                return body
            raise Exception('Unable to fetch template body (code %s) from URL %s' % (response.status_code, url))
        return response.content
    raise Exception('Unable to get template body from input: %s' % req_data)
class ProxyListenerCloudFormation(ProxyListener):
    def forward_request(self, method, path, data, headers):
        if method == 'OPTIONS':
            return 200
        req_data = None
        if method == 'POST' and path == '/':
            req_data = urlparse.parse_qs(to_str(data))
            req_data = dict([(k, v[0]) for k, v in req_data.items()])
            action = req_data.get('Action')
            stack_name = req_data.get('StackName')
            if action == 'CreateStack':
                event_publisher.fire_event(event_publisher.EVENT_CLOUDFORMATION_CREATE_STACK,
                    payload={'n': event_publisher.get_hash(stack_name)})
            if action == 'DeleteStack':
                client = aws_stack.connect_to_service('cloudformation')
                stack_resources = client.list_stack_resources(StackName=stack_name)['StackResourceSummaries']
                template_deployer.delete_stack(stack_name, stack_resources)