Avoid possible NPE warning

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpclient/trunk@1571437 13f79535-47bb-0310-9956-ffa450edef68

httpclient/src/test/java/org/apache/http/localserver/LocalTestServer.java

@@ -310,7 +310,7 @@ public class LocalTestServer {
      */
     public InetSocketAddress getServiceAddress() {
         final ServerSocket ssock = servicedSocket; // avoid synchronization
-        Asserts.check(ssock != null, "Not running");
+        Asserts.notNull(ssock, "Not running");
         return (InetSocketAddress) ssock.getLocalSocketAddress();
     }