HTTP request with XML payload using UrlFetchApp

Is there a way to submit an XML payload with the Google Apps Script URLFetchApp?

I have already tried adding the XML document to the payload

var url = "https://stackoverflow.com"; //not realvar xml = ///some xmlvar params = {'content-type': 'application/xml','method': 'post','payload': xml};var response = UrlFetchApp.fetch(url, params);

I am expecting the request to be submitted, but it errors out at the "fetch".

The error I receive is:

"Attribute provided with invalid value: payload (line 73, file "Code")".