FULL PRODUCT VERSION :
1.8.0_111-b14, Oracle Corporation, Java HotSpot(TM) 64-Bit Server VM

ADDITIONAL OS VERSION INFORMATION :
Windows 7 64-Bit

A DESCRIPTION OF THE PROBLEM :
This is an upstream bug report from:
https://josm.openstreetmap.de/ticket/13964

When calling HttpsURLConnectionImpl.getResponseCode() it is possible to face an NPE with this stacktrace:

=== STACK TRACE ===
Thread: AWT-EventQueue-0 (19) of main
java.lang.NullPointerException
at sun.net.www.protocol.http.HttpURLConnection.getInputStream0(Unknown Source)
at sun.net.www.protocol.http.HttpURLConnection.getInputStream(Unknown Source)
at java.net.HttpURLConnection.getResponseCode(Unknown Source)
at sun.net.www.protocol.https.HttpsURLConnectionImpl.getResponseCode(Unknown Source)
at org.openstreetmap.josm.tools.HttpClient.connect(HttpClient.java:126)
at org.openstreetmap.josm.io.OsmServerReader.getInputStreamRaw(OsmServerReader.java:158)
at org.openstreetmap.josm.io.OsmServerReader.getInputStreamRaw(OsmServerReader.java:110)
at org.openstreetmap.josm.io.OsmServerReader.getInputStream(OsmServerReader.java:74)
at org.openstreetmap.josm.io.OsmServerReader.getInputStream(OsmServerReader.java:57)
at org.openstreetmap.josm.io.BoundingBoxDownloader.parseOsm(BoundingBoxDownloader.java:186)
at org.openstreetmap.josm.actions.downloadtasks.DownloadOsmTask$DownloadTask.parseDataSet(DownloadOsmTask.java:312)
at org.openstreetmap.josm.actions.downloadtasks.DownloadOsmTask$DownloadTask.realRun(DownloadOsmTask.java:320)
at org.openstreetmap.josm.gui.PleaseWaitRunnable.doRealRun(PleaseWaitRunnable.java:93)
at org.openstreetmap.josm.gui.PleaseWaitRunnable.run(PleaseWaitRunnable.java:141)
at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
at java.util.concurrent.FutureTask.run(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)

REPRODUCIBILITY :
This bug can be reproduced rarely.

---------- BEGIN SOURCE ----------
        URL url = new URL("https://...");
        HttpURLConnection connection = (HttpURLConnection) url.openConnection();

        connection.setRequestMethod(requestMethod);
        connection.setRequestProperty("User-Agent", Version.getInstance().getFullAgentString());
        connection.setConnectTimeout(connectTimeout);
        connection.setReadTimeout(readTimeout);
        connection.setInstanceFollowRedirects(false); // we do that ourselves
        if (ifModifiedSince > 0) {
            connection.setIfModifiedSince(ifModifiedSince);
        }
        connection.setUseCaches(useCache);
        if (!useCache) {
            connection.setRequestProperty("Cache-Control", "no-cache");
        }
        for (Map.Entry<String, String> header : headers.entrySet()) {
            if (header.getValue() != null) {
                connection.setRequestProperty(header.getKey(), header.getValue());
            }
        }
        connection.connect();
        int code = connection.getResponseCode(); // <NPE here
---------- END SOURCE ----------