From looking at the same code in WF 10, it looks like it now checks whether one is found before adding the attachment.

JSF application without CDI causes Undertow to crash on deployment ------------------------------------------------------------------ Key: WFLY-4889 URL: https://issues.jboss.org/browse/WFLY-4889 Project: WildFly Issue Type: Bug Components: JSF Affects Versions: 9.0.0.Final Reporter: Ken Finnigan Assignee: Farah Juma My understanding of the JSF spec is that CDI is not a requirement for JSF to function, though there may be some parts of CDI that are required. If I deploy a very simple JSF app to Undertow without CDI, I get the following stack trace: {noformat} Caused by: java.lang.NullPointerException at java.util.concurrent.ConcurrentHashMap.putVal(ConcurrentHashMap.java:1011) at java.util.concurrent.ConcurrentHashMap.putAll(ConcurrentHashMap.java:1084) at io.undertow.servlet.spec.ServletContextImpl.<init>(ServletContextImpl.java:128) at io.undertow.servlet.core.DeploymentManagerImpl.deploy(DeploymentManagerImpl.java:148) at org.wildfly.extension.undertow.deployment.UndertowDeploymentService.startContext(UndertowDeploymentService.java:100) at org.wildfly.extension.undertow.deployment.UndertowDeploymentService$1.run(UndertowDeploymentService.java:82) ... 6 more {noformat} From debugging the value being {{put}} that causes the NPE, it is attempting to add a value of {{null}} for the key {{javax.faces.validator.beanValidator.ValidatorFactory}}. I believe this is a result of https://github.com/wildfly/wildfly/blob/master/jsf/subsystem/src/main/jav... adding the validation factory as a servlet context attribute whether the retrieval found one or not.