Issue #2210 - adding httpclient safety checks.

+ ISE on non started HttpClient
+ ISE on use of wss:// URI with HttpClient without an SSL config

jetty-websocket/websocket-client/src/main/java/org/eclipse/jetty/websocket/client/WebSocketClient.java

@@ -25,6 +25,7 @@ import java.net.URI;
 import java.util.Collections;
 import java.util.HashSet;
 import java.util.Locale;
+import java.util.Objects;
 import java.util.Set;
 import java.util.concurrent.Executor;
 import java.util.concurrent.Future;
@@ -368,6 +369,15 @@ public class WebSocketClient extends ContainerLifeCycle implements WebSocketCont
             throw new IllegalArgumentException("WebSocket URI scheme only supports [ws] and [wss], not [" + scheme + "]");
         }
 
+        if ("wss".equals(scheme))
+        {
+            // test for ssl context
+            if (httpClient.getSslContextFactory() == null)
+            {
+                throw new IllegalStateException("HttpClient has no SslContextFactory, wss:// URI's are not supported in this configuration");
+            }
+        }
+
         request.setRequestURI(toUri);
         request.setLocalEndpoint(websocket);
 
@@ -391,6 +401,17 @@ public class WebSocketClient extends ContainerLifeCycle implements WebSocketCont
         return wsReq.sendAsync();
     }
 
+    @Override
+    protected void doStart() throws Exception
+    {
+        Objects.requireNonNull(httpClient, "Provided HttpClient is null");
+
+        if (!httpClient.isRunning())
+            throw new IllegalStateException("HttpClient is not running (did you forget to start it?): " + httpClient);
+
+        super.doStart();
+    }
+
     @Override
     protected void doStop() throws Exception
     {