NPE with Polymer 2, Flow and @Synchronize annotation

[SomeoneToIgnore]

The following class throws NPE on init:

@Tag("paper-input")
@HtmlImport("bower_components/paper-input/paper-input.html")
// most of the implementation is copied from com.vaadin.hummingbird.html.Input
public class PaperInput extends Component {
    private static final PropertyDescriptor<String, String> valueDescriptor =
            PropertyDescriptors.propertyWithDefault("value", "");

    public PaperInput() {
        // (this public no-arg constructor is required so that Flow can instantiate beans of this type
        // when they are bound to template elements via the @Id() annotation)
    }

    public PaperInput(String value) {
        setValue(value);
    }

    @Synchronize("value-changed")
    public String getValue() {
        return get(valueDescriptor);
    }

    @Synchronize("invalid-changed")
    public String getInvalid() {
        return getElement().getProperty("invalid");
    }

    public void setValue(String value) {
        set(valueDescriptor, value);
    }
}

public class TestUI extends UI {
    @Override
    protected void init(VaadinRequest request) {
        PaperInput paperInput = new PaperInput("sssssss");

        Button button = new Button("Print results", clickEvent -> {
            System.out.println(paperInput.getValue());
            System.out.println(paperInput.getInvalid());
        });
        add(paperInput, button);
    }
}

Fails with NPE.

If we replace new PaperInput("sssssss"); with new PaperInput(); or remove any @Synchronizeannotation, everything works without NPE.

[SomeoneToIgnore]

My understanding is that there are some properties that are synced by default, like value and if we add an extra sync via annotation, we're getting some side effects that cause the NPE.

If we leave the annotation on getInvalid method and remove one on getValue method, all values will be synced without any error.

We need to fix this behaviour, since it's very confusing.

[denis-anisimov]

It's always good to have the stacktrace available in the ticket if exception is mentioned.

[denis-anisimov]

I don't see any NPE.
I see assertion error and unsupported operation exceptions:

java.lang.AssertionError
	at com.vaadin.server.communication.rpc.MapSyncRpcHandler.handleNode(MapSyncRpcHandler.java:48)
	at com.vaadin.server.communication.rpc.AbstractRpcInvocationHandler.handle(AbstractRpcInvocationHandler.java:50)
	at com.vaadin.server.communication.ServerRpcHandler.handleInvocations(ServerRpcHandler.java:370)
	at com.vaadin.server.communication.ServerRpcHandler.handleRpc(ServerRpcHandler.java:296)
	at com.vaadin.server.communication.UidlRequestHandler.synchronizedHandleRequest(UidlRequestHandler.java:87)
	at com.vaadin.server.SynchronizedRequestHandler.handleRequest(SynchronizedRequestHandler.java:40)
	at com.vaadin.server.VaadinService.handleRequest(VaadinService.java:1391)
	at com.vaadin.server.VaadinServlet.service(VaadinServlet.java:277)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
	at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:835)
	at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:583)
	at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:143)
	at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:548)
	at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:226)
	at org.eclipse.jetty.server.handler.ContextHandler.__doHandle(ContextHandler.java:1158)
	at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java)
	at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:511)
	at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:185)
	at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1090)
	at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141)
	at org.eclipse.jetty.server.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:213)
	at org.eclipse.jetty.server.handler.HandlerCollection.handle(HandlerCollection.java:109)
	at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:119)
	at org.eclipse.jetty.server.Server.handle(Server.java:517)
	at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:308)
	at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:242)
	at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:273)
	at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:95)
	at org.eclipse.jetty.io.SelectChannelEndPoint$2.run(SelectChannelEndPoint.java:75)
	at org.eclipse.jetty.util.thread.strategy.ExecuteProduceConsume.produceAndRun(ExecuteProduceConsume.java:213)
	at org.eclipse.jetty.util.thread.strategy.ExecuteProduceConsume.run(ExecuteProduceConsume.java:147)
	at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:654)
	at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:572)
	at java.lang.Thread.run(Thread.java:745)

java.lang.UnsupportedOperationException: FIXME: Implement resync and call it above
	at com.vaadin.server.communication.ServerRpcHandler.handleRpc(ServerRpcHandler.java:291)
	at com.vaadin.server.communication.UidlRequestHandler.synchronizedHandleRequest(UidlRequestHandler.java:87)
	at com.vaadin.server.SynchronizedRequestHandler.handleRequest(SynchronizedRequestHandler.java:40)
	at com.vaadin.server.VaadinService.handleRequest(VaadinService.java:1391)
	at com.vaadin.server.VaadinServlet.service(VaadinServlet.java:277)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
	at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:835)
	at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:583)
	at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:143)
	at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:548)
	at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:226)
	at org.eclipse.jetty.server.handler.ContextHandler.__doHandle(ContextHandler.java:1158)
	at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java)
	at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:511)
	at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:185)
	at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1090)
	at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141)
	at org.eclipse.jetty.server.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:213)
	at org.eclipse.jetty.server.handler.HandlerCollection.handle(HandlerCollection.java:109)
	at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:119)
	at org.eclipse.jetty.server.Server.handle(Server.java:517)
	at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:308)
	at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:242)
	at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:273)
	at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:95)
	at org.eclipse.jetty.io.SelectChannelEndPoint$2.run(SelectChannelEndPoint.java:75)
	at org.eclipse.jetty.util.thread.strategy.ExecuteProduceConsume.produceAndRun(ExecuteProduceConsume.java:213)
	at org.eclipse.jetty.util.thread.strategy.ExecuteProduceConsume.run(ExecuteProduceConsume.java:147)
	at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:654)
	at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:572)
	at java.lang.Thread.run(Thread.java:745)

[denis-anisimov]

Alright, I have assertions enabled that's why I get assertion exception before NPE.
With disabled assertions there won't be assertion error but NPE will be thrown instead later on.

[denis-anisimov]

I don't see any difference with @Synchronized or without by the way.

Original problem here is on the client side. Property sync message (mSync) always has to contain value for the property . It doesn't. The reason: something happened on the client side which prevents to set this property into transport JSON object. And there is a client side exception.