I am using the **latest** localstack docker image to test aws s3, lambda and cloudformation locally. s3 and lambda seems to be working fine but when I call cloudformation **create-stack** api it gives me a 502 BadGateway error. This is the command I am using

`aws cloudformation create-stack \
  --template-body template.yaml \
  --stack-name cfn-test \
  --parameters ParameterKey=BucketPrefix,ParameterValue=demo-bucket \
  --endpoint-url=http://localhost:4581`

This is the error I get:
`An error occurred (502) when calling the CreateStack operation (reached max retries: 4): Bad Gateway`

From docker logs I got the following error
`2019-12-31T22:12:09:ERROR:localstack.services.generic_proxy: Error forwarding request: 'str' object has no attribute 'get' Traceback (most recent call last):
  File "/opt/code/localstack/localstack/services/generic_proxy.py", line 242, in forward
    path=path, data=data, headers=forward_headers)
  File "/opt/code/localstack/localstack/services/cloudformation/cloudformation_listener.py", line 164, in forward_request
    modified_request = transform_template(req_data)
  File "/opt/code/localstack/localstack/services/cloudformation/cloudformation_listener.py", line 83, in transform_template
    if parsed.get('Transform') == 'AWS::Serverless-2016-10-31':
AttributeError: 'str' object has no attribute 'get'`

Although, when I try the **list-stacks** api it seems to be working fine
`aws --endpoint-url=http://localhost:4581 cloudformation list-stacks`

`{
    "StackSummaries": []
}`

`2019-12-31 22:10:51,865:API: 127.0.0.1 - - [31/Dec/2019 22:10:51] "GET / HTTP/1.1" 200 -`

I could not find a solution in any of the past issues or anywhere on the internet. Please assist
import re
import os
import json
import yaml
import logging
import traceback
import moto.cloudformation.utils
from six import iteritems
from six import string_types
from localstack.utils import common
from localstack.utils.aws import aws_stack
from localstack.utils.testutil import create_zip_file
from localstack.services.awslambda.lambda_api import get_handler_file_from_name
ACTION_CREATE = 'create'
ACTION_DELETE = 'delete'
PLACEHOLDER_RESOURCE_NAME = '__resource_name__'
LOG = logging.getLogger(__name__)
UPDATEABLE_RESOURCES = ['Lambda::Function', 'ApiGateway::Method']
STATIC_REFS = ['AWS::Region', 'AWS::Partition', 'AWS::StackName']
NoDatesSafeLoader = yaml.SafeLoader
NoDatesSafeLoader.yaml_implicit_resolvers = {
    k: [r for r in v if r[0] != 'tag:yaml.org,2002:timestamp'] for
    k, v in NoDatesSafeLoader.yaml_implicit_resolvers.items()
}
def str_or_none(o):