code: function toLambdaProxyResponse(statusCode, headers, body, defaultHeaders) {
    const proxyResponse = {statusCode: statusCode};
  
    const headersWithDefaults = headers && defaultHeaders ? merge(defaultHeaders, copy(headers)) :
      headers || (defaultHeaders && copy(defaultHeaders));
    if (headersWithDefaults) {
      proxyResponse.headers = headersWithDefaults;
    }
  
    proxyResponse.body = isString(body) ? body : stringify(body);
  
    return proxyResponse;
  }
docs: Builds & returns a Lambda Proxy integration compatible response.
  @param {number|string} statusCode - the HTTP status code to return
  @param {Object|undefined} [headers] - optional response headers to use
  @param {Object|string|undefined} [body] - an optional response body to use
  @param {Object|undefined} [defaultHeaders] - optional default custom headers to be included in the Lambda Proxy response
  @return {{statusCode: (number|string), headers: (Object|undefined), body: (string|undefined)}} a Lambda Proxy response