HttpClient tunnel creation assumes when it gets the server response t…

…hat the request always sent headers and the headers multimap is never null which leads to an NPE when no headers was sent. - fixes #4074

src/main/java/io/vertx/core/http/impl/Http1xClientConnection.java

@@ -744,7 +744,7 @@ private void handleResponseBegin(Stream stream, HttpResponseHead response) {
         if ((request.method == HttpMethod.CONNECT &&
              response.statusCode == 200) || (
              request.method == HttpMethod.GET &&
-             request.headers.contains("connection", "Upgrade", false) &&
+             request.headers != null && request.headers.contains("connection", "Upgrade", false) &&
              response.statusCode == 101)) {
           removeChannelHandlers();
         }

src/test/java/io/vertx/core/http/HttpTest.java

@@ -5367,6 +5367,34 @@ public void testHttpInvalidConnectResponseChunked() {
     await();
   }
 
+  @Test
+  public void testUpgradeTunnelNoSwitch() throws Exception {
+    server.requestHandler(req -> {
+      HttpServerResponse resp = req.response();
+      resp.setChunked(true);
+      resp.write("chunk-1")
+        .compose(v -> resp.write("chunk-2"))
+        .compose(v -> resp.end("chunk-3"));
+    });
+
+    startServer();
+
+    client.request(HttpMethod.GET, DEFAULT_HTTP_PORT, DEFAULT_HTTP_HOST, "/", onSuccess(req -> {
+      req.connect(onSuccess(resp -> {
+        assertEquals(200, resp.statusCode());
+        List<String> chunks = new ArrayList<>();
+        resp.handler(chunk -> {
+          chunks.add(chunk.toString());
+        });
+        resp.endHandler(v -> {
+          assertEquals(Arrays.asList("chunk-1", "chunk-2", "chunk-3"), chunks);
+          testComplete();
+        });
+      }));
+    }));
+    await();
+  }
+
   @Test
   public void testEndFromAnotherThread() throws Exception {
     waitFor(2);