Fixes #2821 - AuthenticationProtocolHandler should not always cache Authentication.Result.

Now the Result is cached only if getURI() returns non-null.

jetty-client/src/main/java/org/eclipse/jetty/client/HttpAuthenticationStore.java

@@ -65,7 +65,9 @@ public class HttpAuthenticationStore implements AuthenticationStore
     @Override
     public void addAuthenticationResult(Authentication.Result result)
     {
-        results.put(result.getURI(), result);
+        URI uri = result.getURI();
+        if (uri != null)
+            results.put(uri, result);
     }
 
     @Override