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

Estaba montando JCS en mi proyecto web donde tengo Strut 1.3 agregando la dependencia de Maven:

<dependency>
  <groupId>jcs</groupId>
  <artifactId>jcs</artifactId>
  <version>1.3</version>
</dependency>

Y de repente comencé a tener la siguiente excepción al inicializar la aplicación en Tomcat:

2010-09-28 10:44:36 ERROR [ContainerBackgroundProcessor[StandardEngine[Catalina]]] (Digester.java:789) - Digester.getParser:
java.lang.UnsupportedOperationException: This parser does not support specification "null" version "null"
at javax.xml.parsers.SAXParserFactory.setXIncludeAware(SAXParserFactory.java:448)
at org.apache.commons.digester.Digester.getFactory(Digester.java:534)
at org.apache.commons.digester.Digester.getParser(Digester.java:786)
at org.apache.commons.digester.Digester.getXMLReader(Digester.java:1058)
at org.apache.commons.digester.Digester.parse(Digester.java:1887)
at org.apache.struts.action.ActionServlet.initServlet(ActionServlet.java:1144)
at org.apache.struts.action.ActionServlet.init(ActionServlet.java:328)
at javax.servlet.GenericServlet.init(GenericServlet.java:212)
at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1173)
at org.apache.catalina.core.StandardWrapper.load(StandardWrapper.java:993)
at org.apache.catalina.core.StandardContext.loadOnStartup(StandardContext.java:4187)
at org.apache.catalina.core.StandardContext.start(StandardContext.java:4496)
at org.apache.catalina.core.StandardContext.reload(StandardContext.java:3228)
at org.apache.catalina.loader.WebappLoader.backgroundProcess(WebappLoader.java:403)
at org.apache.catalina.core.ContainerBase.backgroundProcess(ContainerBase.java:1309)
at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.processChildren(ContainerBase.java:1601)
at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.processChildren(ContainerBase.java:1610)
at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.processChildren(ContainerBase.java:1610)
at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.run(ContainerBase.java:1590)
at java.lang.Thread.run(Thread.java:619)

Después de investigar un poco en Google descubrí una dependencia de JCS estaba causando este conflicto: Xerces

Así que aprendí algo nuevo del pom.xml, cómo agregar una exclusión:

<dependency>
  <groupId>jcs</groupId>
  <artifactId>jcs</artifactId>
  <version>1.3</version>
  <exclusions>
     <exclusion>
        <groupId>xerces</groupId>
        <artifactId>xercesImpl</artifactId>
     </exclusion>
  </exclusions>
</dependency>