Multiple Autocomplete with a value of a list of strings can't generate Converter JSF?

Question

I am currently working on a project and I need tags for questions (like the stackoverflow tags) so I am using a multiple autocomplete (it is an h:form):

<p:autoComplete id="autoComplete" value="#{questionMB.tags}" completeMethod="#{questionMB.complete}" multiple="true" forceSelection="true" unique="true" />

This is the questionMB

@Named
@ViewScoped
@RolesAllowed(value = { "ADMIN", "SUPERUSER", "USER" })
public class questionMB implements Serializable {

    private static final long serialVersionUID = -4130025302903207410L;
    private List<String> tags = new ArrayList<>();
    //other vars...

    public List<String> complete(String query) {
        //retrieves data from database
        return DBHelper.completeTag(query);
    }

    //other functions, getters and setter...
}

When I am using this it throws this Exception:

20:47:21,418 SEVERE [javax.enterprise.resource.webcontainer.jsf.application] (default task-8) Error Rendering View[/user/postRepair.xhtml]: java.lang.NullPointerException
at com.sun.faces.cdi.CdiUtils.createConverter(CdiUtils.java:102)
at com.sun.faces.application.applicationimpl.InstanceFactory.createConverter(InstanceFactory.java:481)
at com.sun.faces.application.ApplicationImpl.createConverter(ApplicationImpl.java:510)
at javax.faces.application.ApplicationWrapper.createConverter(ApplicationWrapper.java:431)
at org.omnifaces.cdi.converter.ConverterManager.createConverter(ConverterManager.java:155)
at org.omnifaces.cdi.converter.ConverterManager$Proxy$_$$_WeldClientProxy.createConverter(Unknown Source)
at org.omnifaces.application.OmniApplication.createConverter(OmniApplication.java:98)
at org.primefaces.util.ComponentUtils.getConverter(ComponentUtils.java:175)
at org.primefaces.component.autocomplete.AutoCompleteRenderer.encodeSuggestions(AutoCompleteRenderer.java:481)
at org.primefaces.component.autocomplete.AutoCompleteRenderer.encodeResults(AutoCompleteRenderer.java:136)
at org.primefaces.component.autocomplete.AutoCompleteRenderer.encodeEnd(AutoCompleteRenderer.java:117)
at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:595)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1654)
at com.sun.faces.context.PartialViewContextImpl$PhaseAwareVisitCallback.visit(PartialViewContextImpl.java:615)
at com.sun.faces.component.visit.PartialVisitContext.invokeVisitCallback(PartialVisitContext.java:159)
at javax.faces.component.UIComponent.visitTree(UIComponent.java:1456)
at javax.faces.component.UIComponent.visitTree(UIComponent.java:1468)
at javax.faces.component.UIComponent.visitTree(UIComponent.java:1468)
at javax.faces.component.UIComponent.visitTree(UIComponent.java:1468)
at javax.faces.component.UIForm.visitTree(UIForm.java:355)
at javax.faces.component.UIComponent.visitTree(UIComponent.java:1468)
at javax.faces.component.UIComponent.visitTree(UIComponent.java:1468)
at javax.faces.component.UIComponent.visitTree(UIComponent.java:1468)
at com.sun.faces.context.PartialViewContextImpl.processComponents(PartialViewContextImpl.java:400)
at com.sun.faces.context.PartialViewContextImpl.processPartial(PartialViewContextImpl.java:319)
at org.primefaces.context.PrimePartialViewContext.processPartial(PrimePartialViewContext.java:63)
at javax.faces.context.PartialViewContextWrapper.processPartial(PartialViewContextWrapper.java:228)
at org.omnifaces.context.OmniPartialViewContext.processPartial(OmniPartialViewContext.java:122)
at javax.faces.component.UIViewRoot.encodeChildren(UIViewRoot.java:1101)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1647)
at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:442)
at com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:170)
at javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:132)
at javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:132)
at javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:132)
at org.omnifaces.viewhandler.OmniViewHandler.renderView(OmniViewHandler.java:115)
at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:102)
at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:76)
at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:199)
at javax.faces.webapp.FacesServlet.executeLifecyle(FacesServlet.java:708)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:451)
at io.undertow.servlet.handlers.ServletHandler.handleRequest(ServletHandler.java:74)
at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:129)
at org.omnifaces.filter.GzipResponseFilter.doFilter(GzipResponseFilter.java:181)
at org.omnifaces.filter.HttpFilter.doFilter(HttpFilter.java:108)
at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61)
at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131)
at com.github.adminfaces.template.session.AdminFilter.doFilter(AdminFilter.java:128)
at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61)
at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131)
at io.opentracing.contrib.jaxrs2.server.SpanFinishingFilter.doFilter(SpanFinishingFilter.java:55)
at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61)
at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131)
at io.undertow.servlet.handlers.FilterHandler.handleRequest(FilterHandler.java:84)
at io.undertow.servlet.handlers.security.ServletSecurityRoleHandler.handleRequest(ServletSecurityRoleHandler.java:62)
at io.undertow.servlet.handlers.ServletChain$1.handleRequest(ServletChain.java:68)
at io.undertow.servlet.handlers.ServletDispatchingHandler.handleRequest(ServletDispatchingHandler.java:36)
at org.wildfly.extension.undertow.security.SecurityContextAssociationHandler.handleRequest(SecurityContextAssociationHandler.java:78)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at io.undertow.servlet.handlers.security.SSLInformationAssociationHandler.handleRequest(SSLInformationAssociationHandler.java:132)
at io.undertow.servlet.handlers.security.ServletAuthenticationCallHandler.handleRequest(ServletAuthenticationCallHandler.java:57)
at io.undertow.server.handlers.DisableCacheHandler.handleRequest(DisableCacheHandler.java:33)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at io.undertow.security.handlers.AuthenticationConstraintHandler.handleRequest(AuthenticationConstraintHandler.java:53)
at io.undertow.security.handlers.AbstractConfidentialityHandler.handleRequest(AbstractConfidentialityHandler.java:46)
at io.undertow.servlet.handlers.security.ServletConfidentialityConstraintHandler.handleRequest(ServletConfidentialityConstraintHandler.java:64)
at io.undertow.servlet.handlers.security.ServletSecurityConstraintHandler.handleRequest(ServletSecurityConstraintHandler.java:59)
at io.undertow.security.handlers.AuthenticationMechanismsHandler.handleRequest(AuthenticationMechanismsHandler.java:60)
at io.undertow.servlet.handlers.security.CachedAuthenticatedSessionHandler.handleRequest(CachedAuthenticatedSessionHandler.java:77)
at io.undertow.security.handlers.NotificationReceiverHandler.handleRequest(NotificationReceiverHandler.java:50)
at io.undertow.security.handlers.AbstractSecurityContextAssociationHandler.handleRequest(AbstractSecurityContextAssociationHandler.java:43)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at org.wildfly.extension.undertow.security.jacc.JACCContextIdHandler.handleRequest(JACCContextIdHandler.java:61)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at org.wildfly.extension.undertow.security.jaspi.JASPICSecureResponseHandler.handleRequest(JASPICSecureResponseHandler.java:48)
at org.wildfly.extension.undertow.deployment.GlobalRequestControllerHandler.handleRequest(GlobalRequestControllerHandler.java:68)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at io.undertow.servlet.handlers.ServletInitialHandler.handleFirstRequest(ServletInitialHandler.java:292)
at io.undertow.servlet.handlers.ServletInitialHandler.access$100(ServletInitialHandler.java:81)
at io.undertow.servlet.handlers.ServletInitialHandler$2.call(ServletInitialHandler.java:138)
at io.undertow.servlet.handlers.ServletInitialHandler$2.call(ServletInitialHandler.java:135)
at io.undertow.servlet.core.ServletRequestContextThreadSetupAction$1.call(ServletRequestContextThreadSetupAction.java:48)
at io.undertow.servlet.core.ContextClassLoaderSetupAction$1.call(ContextClassLoaderSetupAction.java:43)
at org.wildfly.extension.undertow.security.SecurityContextThreadSetupAction.lambda$create$0(SecurityContextThreadSetupAction.java:105)
at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create$0(UndertowDeploymentInfoService.java:1502)
at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create$0(UndertowDeploymentInfoService.java:1502)
at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create$0(UndertowDeploymentInfoService.java:1502)
at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create$0(UndertowDeploymentInfoService.java:1502)
at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:272)
at io.undertow.servlet.handlers.ServletInitialHandler.access$000(ServletInitialHandler.java:81)
at io.undertow.servlet.handlers.ServletInitialHandler$1.handleRequest(ServletInitialHandler.java:104)
at io.undertow.server.Connectors.executeRootHandler(Connectors.java:364)
at io.undertow.server.HttpServerExchange$1.run(HttpServerExchange.java:830)
at org.jboss.threads.ContextClassLoaderSavingRunnable.run(ContextClassLoaderSavingRunnable.java:35)
at org.jboss.threads.EnhancedQueueExecutor.safeRun(EnhancedQueueExecutor.java:1982)
at org.jboss.threads.EnhancedQueueExecutor$ThreadBody.doRunTask(EnhancedQueueExecutor.java:1486)
at org.jboss.threads.EnhancedQueueExecutor$ThreadBody.run(EnhancedQueueExecutor.java:1377)
at java.lang.Thread.run(Unknown Source)

There is no problem with anything else because when I remove the value="#{questionMB.tags}" it works completely fine, so I can remove, add and search for tags. But when I add the value: I enter one character (the DBHelper.completeTag() still works correct and returns values which are just not shown in the UI) and the exception is thrown.

So the problem seems to be that no converter can be generated (just see line 2 in stacktrace). So I thought it should be no problem converting it because I am only using strings. Maybe there is a problem with the list and it cannot be converted. So I searched for two days and I could not find a single problem that can answer mine.

EDIT

I already tested which components are null: DBHelper.completeTag() returns a fine list of strings with the correct value from the Database. List<String> tags = new ArrayList<>(); initializes the list of tags but with no String values (not null).

I am using Primefaces 7.0, OmniFaces 3.2, Mojarra and Primefaces-Extensions 6.1.1.

Answer 1

As found out by @Kukeltje, this is a known issue: NPE when determining converter for primitive values.

The workaround is said to be installing omnifaces 3.3.

The actual fix is scheduled for Mojarra 2.3.10 release - the reference implementation of Jakarta Faces.

---

Yesterday I suggested in a comment someone should write this answer but the comment was deleted, so here I go dispite the fact this is not my finding. Feel free to write another answer, this is not ment for reputation harvesting but a signpost for others encountering this issue. While madly one gets no feedback for deleted comments, I guess it was deleted because I hintet that the OP is surely not using Version 8 of Mojarra in a sarcastic way. Sorry if someone felt offended.