SEVERE: Parse error in application web.xml file at jndi:/localhost/demo/WEB-INF/web.xml
Throwable occurred: java.lang.NumberFormatException: For input string: ""
        at org.apache.tomcat.util.digester.Digester.createSAXException(Digester.java:2687)
        at org.apache.tomcat.util.digester.Digester.createSAXException(Digester.java:2713)
        at org.apache.tomcat.util.digester.Digester.endElement(Digester.java:1060)
        at org.apache.xerces.parsers.AbstractSAXParser.endElement(Unknown Source)
        at org.apache.xerces.parsers.AbstractXMLDocumentParser.emptyElement(Unknown Source)
        at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl.scanStartElement(Unknown Source)
        at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl$FragmentContentDispatcher.dispatch(Unknown Source)
        at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl.scanDocument(Unknown Source)
        at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)
        at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)
        at org.apache.xerces.parsers.XMLParser.parse(Unknown Source)
        at org.apache.xerces.parsers.AbstractSAXParser.parse(Unknown Source)
        at org.apache.xerces.jaxp.SAXParserImpl$JAXPSAXParser.parse(Unknown Source)
        at org.apache.tomcat.util.digester.Digester.parse(Digester.java:1543)
        at org.apache.catalina.startup.ContextConfig.parseWebXml(ContextConfig.java:1685)
        at org.apache.catalina.startup.ContextConfig.webConfig(ContextConfig.java:1201)
        at org.apache.catalina.startup.ContextConfig.configureStart(ContextConfig.java:874)
        at org.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:317)
        at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:119)
        at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:89)
        at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:4974)
        at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145)
        at org.apache.catalina.manager.ManagerServlet.start(ManagerServlet.java:1284)
        at org.apache.catalina.manager.HTMLManagerServlet.start(HTMLManagerServlet.java:735

...


        <servlet>
                <servlet-name>NavModelRegisterServlet</servlet-name>
                <servlet-class>xxx</servlet-class>
                <load-on-startup/>
        </servlet>


(resolved by changing to  <load-on-startup>1</load-on-startup> but not <load-on-startup></load-on-startup>)