Merge the values of headers and multiValueHeaders into a single dict.
    Opens up support for multivalue headers via API Gateway and ALB.
    See: https://github.com/Miserlou/Zappa/pull/1756

def merge_headers(event):
    """
    Merge the values of headers and multiValueHeaders into a single dict.
    Opens up support for multivalue headers via API Gateway and ALB.
    See: https://github.com/Miserlou/Zappa/pull/1756
    """
    headers = event.get('headers') or {}
    multi_headers = (event.get('multiValueHeaders') or {}).copy()
    for h in set(headers.keys()):
        if h not in multi_headers:
            multi_headers[h] = [headers[h]]
    for h in multi_headers.keys():
        multi_headers[h] = ', '.join(multi_headers[h])
    return multi_headers