Type of request: This is a ...

[ X ] bug report
[ ] feature request

Detailed description

Issue originally described and fixed here #2055 has been reverted by a subsequent change. This PR reverted the fix: #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