Jenkins Groovy HttpURLConnection PUT request failing while creating writer

Question

So I'm trying to make a put request with HttpURLConnection in a groovy script running inside Jenkins. I have successfully made get and post calls with url-encoded-data, but the put request with a JSON body is not working. I've tried many solutions with no success.

Here is my current code with debugging prints:

        URL url = null;
        InputStream stream = null;
        HttpURLConnection urlConnection = null;
        jenkins.println("Enter try block...")
        try {
            url = new URL(urlString);
            urlConnection = (HttpURLConnection) url.openConnection();
            jenkins.println("Open connection...")
            urlConnection.setRequestMethod("PUT");
//            urlConnection.setRequestProperty("Content-Type", "application/json")
            urlConnection.setRequestProperty("Authorization", "Bearer " + token)
            urlConnection.setRequestProperty("Accept", "application/json")
            urlConnection.setDoOutput(false);
            urlConnection.setDoInput(true);

            urlConnection.connect();

            jenkins.println("Connect...")
            OutputStream writer = urlConnection.getOutputStream()
//            OutputStreamWriter writer = new OutputStreamWriter(urlConnection.getOutputStream());
            jenkins.println("Created writer...")
            byte[] outputInBytes = data.getBytes("UTF-8")
            writer.write(outputInBytes)
//            writer.write(data)
            jenkins.println("wrote data...")
            writer.flush()
            jenkins.println("flushed...")
            writer.close()
            jenkins.println("writer closed...")


            jenkins.println("------- Print response codes and message -------")
            jenkins.println(urlConnection.getResponseCode())
            jenkins.println(urlConnection.getResponseMessage())

            jenkins.println("Begin input stream...")
            stream = urlConnection.getInputStream()
            BufferedReader reader = new BufferedReader(new InputStreamReader(stream, "UTF-8"), 8);
            String result = reader.readLine();
            jenkins.println(JsonHelper.parse(result))
            return JsonHelper.parse(result)

The Jenkins output is:

Incoming json is: {
    "name": "Signature-Verification",
    "owningTeam": 281,
    "customFields": [
        {
            "id": 2,
            "value": "My team is awesome"
        },
        {
            "id": 3,
            "value": "apitesttothemoon"
        }
    ]
}
[Pipeline] echo
Enter try block...
[Pipeline] echo
Open connection...
[Pipeline] echo
Connect...
[Pipeline] echo
null
[Pipeline] End of Pipeline
Finished: SUCCESS

Based on the logs I know it's failing at the creation of the writer. I just don't know why. The writer creates and works fine for the url-encoded post requests, but not the put.

Any insight is appreciated. I've put several hours into this and don't know where to go next.