java.lang.UnsupportedOperationException: This parser does not support specification "null" version "null"

Issue

I'm using Apache Struts and Commons Digester. When I deploy my application, I get this error in EAP 6:

java.lang.UnsupportedOperationException: This parser does not support specification "null" version "null"
    at javax.xml.parsers.SAXParserFactory.setSchema(SAXParserFactory.java:419) [rt.jar:1.7.0_65]
    at __redirected.__SAXParserFactory.setSchema(__SAXParserFactory.java:154) [jboss-modules.jar:1.2.0.Final-redhat-1]
    at org.apache.commons.digester.Digester.getFactory(Digester.java:541) [commons-digester-2.1.jar:2.1]
    at org.apache.commons.digester.Digester.getParser(Digester.java:791) [commons-digester-2.1.jar:2.1]
    at org.apache.commons.digester.Digester.getXMLReader(Digester.java:1068) [commons-digester-2.1.jar:2.1]
    at org.apache.commons.digester.Digester.parse(Digester.java:1916) [commons-digester-2.1.jar:2.1]
    at org.apache.struts.action.ActionServlet.initServlet(ActionServlet.java:1785) [struts-core-1.3.10.jar:1.3.10]
    at org.apache.struts.action.ActionServlet.init(ActionServlet.java:349) [struts-core-1.3.10.jar:1.3.10]
    at javax.servlet.GenericServlet.init(GenericServlet.java:242) [jboss-servlet-api_3.0_spec-1.0.2.Final-redhat-1.jar:1.0.2.Final-redhat-1]
    at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1194) [jbossweb-7.2.0.Final-redhat-1.jar:7.2.0.Final-redhat-1]
    at org.apache.catalina.core.StandardWrapper.load(StandardWrapper.java:1100) [jbossweb-7.2.0.Final-redhat-1.jar:7.2.0.Final-redhat-1]
    at org.apache.catalina.core.StandardContext.loadOnStartup(StandardContext.java:3591) [jbossweb-7.2.0.Final-redhat-1.jar:7.2.0.Final-redhat-1]
    at org.apache.catalina.core.StandardContext.start(StandardContext.java:3798) [jbossweb-7.2.0.Final-redhat-1.jar:7.2.0.Final-redhat-1]
    at org.jboss.as.web.deployment.WebDeploymentService.doStart(WebDeploymentService.java:156) [jboss-as-web-7.2.0.Final-redhat-8.jar:7.2.0.Final-redhat-8]
    at org.jboss.as.web.deployment.WebDeploymentService.access$000(WebDeploymentService.java:60) [jboss-as-web-7.2.0.Final-redhat-8.jar:7.2.0.Final-redhat-8]
    at org.jboss.as.web.deployment.WebDeploymentService$1.run(WebDeploymentService.java:93) [jboss-as-web-7.2.0.Final-redhat-8.jar:7.2.0.Final-redhat-8]
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471) [rt.jar:1.7.0_65]
    at java.util.concurrent.FutureTask.run(FutureTask.java:262) [rt.jar:1.7.0_65]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) [rt.jar:1.7.0_65]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) [rt.jar:1.7.0_65]
    at java.lang.Thread.run(Thread.java:745) [rt.jar:1.7.0_65]
    at org.jboss.threads.JBossThread.run(JBossThread.java:122)

Note that this issue can occur even if Struts or Digester aren't used. The application only needs to invoke SAXParserFactory.setSchema().