how to remove a header from URLConnection

I am talking to a file upload service that accepts post data, not form data. By default, java's HttpURLConnection sets the Content-Type header to application/x-www-form-urlencoded. this is obviously wrong if i'm posting pure data.

I (the client) don't know the content type. I don't want the Content-Type header set at all. the service has a feature where it will guess at the content type (based on the file name, reading some data from the file, etc).

How do I unset a header? There's no remove header, and setting it to null doesn't change the value and setting it to the empty string results in the header being set with no value.