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# Type of request: This is a ...

[ X ] bug report
[ ] feature request

# Detailed description
Issue originally described and fixed here https://github.com/localstack/localstack/issues/2055 has been reverted by a subsequent change. This PR reverted the fix: https://github.com/localstack/localstack/pull/2202 on file apigateway_listener.py

See original issue for full details.

## Actual behaviour

Serverless Lambda gives a 502 bad gateway response.

`localstack_1  | 2020-04-06T16:03:43:ERROR:localstack.services.generic_proxy: Error forwarding request: 'NoneType' object is not iterable Traceback (most recent call last):
localstack_1  |   File "/opt/code/localstack/localstack/services/generic_proxy.py", line 247, in forward
localstack_1  |     listener_result = listener.forward_request(method=method,
localstack_1  |   File "/opt/code/localstack/localstack/services/apigateway/apigateway_listener.py", line 47, in forward_request
localstack_1  |     return invoke_rest_api(api_id, stage, method, relative_path_w_query_params, data, headers, path=path)
localstack_1  |   File "/opt/code/localstack/localstack/services/apigateway/apigateway_listener.py", line 254, in invoke_rest_api
localstack_1  |     response.headers.update((parsed_result or {}).get('headers', {}))
localstack_1  |   File "/usr/lib/python3.8/_collections_abc.py", line 837, in update
localstack_1  |     for key, value in other:
localstack_1  | TypeError: 'NoneType' object is not iterable
`
if re.match(r'/restapis/[^/]+/documentation/versions', path):
            if response.status_code == 404:
                return requests_response({'position': '1', 'items': []})
        
        if method == 'POST' and path == '/restapis':
            content = json.loads(to_str(response.content))
            event_publisher.fire_event(event_publisher.EVENT_APIGW_CREATE_API,
                payload={'a': event_publisher.get_hash(content['id'])})
        api_regex = r'^/restapis/([a-zA-Z0-9\-]+)$'
        if method == 'DELETE' and re.match(api_regex, path):
            api_id = re.sub(api_regex, r'\1', path)
            event_publisher.fire_event(event_publisher.EVENT_APIGW_DELETE_API,
                payload={'a': event_publisher.get_hash(api_id)})
def get_gateway_responses(api_id):