As described in WFLY-2897, if a Mojarra 2.2.x implementation JAR is accidentally included in a JSF application's WAR file, the following error occurs when deploying the application to WildFly:

11:22:36,630 SEVERE [javax.enterprise.resource.webcontainer.jsf.config] (MSC service thread 1-6) Critical error during deployment: : com.sun.faces.config.ConfigurationException: 
        The tag named passThroughAttribute from namespace http://xmlns.jcp.org/jsf/core has a null handler-class defined
        at com.sun.faces.config.processor.FaceletTaglibConfigProcessor.processHandlerClass(FaceletTaglibConfigProcessor.java:422) [jsf-impl-2.2.5-jbossorg-3.jar:]
        at com.sun.faces.config.processor.FaceletTaglibConfigProcessor.processTags(FaceletTaglibConfigProcessor.java:378) [jsf-impl-2.2.5-jbossorg-3.jar:]
        at com.sun.faces.config.processor.FaceletTaglibConfigProcessor.processTagLibrary(FaceletTaglibConfigProcessor.java:321) [jsf-impl-2.2.5-jbossorg-3.jar:]
        at com.sun.faces.config.processor.FaceletTaglibConfigProcessor.process(FaceletTaglibConfigProcessor.java:270) [jsf-impl-2.2.5-jbossorg-3.jar:]
        at com.sun.faces.config.ConfigManager.initialize(ConfigManager.java:437) [jsf-impl-2.2.5-jbossorg-3.jar:]
        at com.sun.faces.config.ConfigureListener.contextInitialized(ConfigureListener.java:214) [jsf-impl-2.2.5-jbossorg-3.jar:]
        at io.undertow.servlet.core.ApplicationListeners.contextInitialized(ApplicationListeners.java:173) [undertow-servlet-1.0.1.Final.jar:1.0.1.Final]
        at io.undertow.servlet.core.DeploymentManagerImpl.deploy(DeploymentManagerImpl.java:189) [undertow-servlet-1.0.1.Final.jar:1.0.1.Final]
        at org.wildfly.extension.undertow.deployment.UndertowDeploymentService.startContext(UndertowDeploymentService.java:86)
        at org.wildfly.extension.undertow.deployment.UndertowDeploymentService.start(UndertowDeploymentService.java:71)
        at org.jboss.msc.service.ServiceControllerImpl$StartTask.startService(ServiceControllerImpl.java:1948)
        at org.jboss.msc.service.ServiceControllerImpl$StartTask.run(ServiceControllerImpl.java:1881)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) [rt.jar:1.7.0_17]
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) [rt.jar:1.7.0_17]
        at java.lang.Thread.run(Thread.java:722) [rt.jar:1.7.0_17]

To fix this, simply remove the Mojarra 2.2.x implementation JAR from the JSF application's WAR file.