Unable to parse document faces-config.xml in JSF application

I'm developing a JSF web app. I use JSF 2.2 with Apache Tomcat 8.0.27.0. When I press clean & build it works ok, but when I try to run my app I get this exception:
     com.sun.faces.config.ConfigurationException: java.util.concurrent.ExecutionException: com.sun.faces.config.ConfigurationException: Unable to parse document 'file:/C:/Users/axeli/Desktop/SeminarioPagina/build/web/WEB-INF/faces-config.xml': null

    28-Feb-2016 18:00:19.275 INFO [http-nio-8084-exec-10] org.apache.catalina.util.LifecycleBase.stop The stop() method was called on component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[]] after stop() had already been called. The second call will be ignored.
    28-Feb-2016 18:00:19.777 INFO [http-nio-8084-exec-10] org.apache.catalina.startup.HostConfig.undeploy Repliegue (undeploy) de la aplicación web que tiene como trayectoria de contexto 
    28-Feb-2016 18:00:19.878 INFO [http-nio-8084-exec-10] org.apache.catalina.startup.HostConfig.deployDescriptor Desplieque del descriptor de configuración C:\Users\axeli\AppData\Roaming\NetBeans\8.1\apache-tomcat-8.0.27.0_base\conf\Catalina\localhost\ROOT.xml
    28-Feb-2016 18:00:19.878 WARNING [http-nio-8084-exec-10] org.apache.catalina.startup.SetContextPropertiesRule.begin [SetContextPropertiesRule]{Context} Setting property 'antiJARLocking' to 'true' did not find a matching property.
    28-Feb-2016 18:00:20.826 INFO [http-nio-8084-exec-10] org.apache.jasper.servlet.TldScanner.scanJars Al menos un JAR, que se ha explorado buscando TLDs, aún no contenía TLDs. Activar historial de depuración para este historiador para una completa lista de los JARs que fueron explorados y de los que nos se halló TLDs. Saltarse JARs no necesarios durante la exploración puede dar lugar a una mejora de tiempo significativa en el arranque y compilación de JSP .
    28-Feb-2016 18:00:20.948 INFO [http-nio-8084-exec-10] com.sun.faces.config.ConfigureListener.contextInitialized Inicializando Mojarra 2.2.7 ( 20140610-1547 https://svn.java.net/svn/mojarra~svn/tags/2.2.7@13362) para el contexto ''
    28-Feb-2016 18:00:21.079 SEVERE [http-nio-8084-exec-10] com.sun.faces.config.ConfigureListener.contextInitialized Critical error during deployment: 
     com.sun.faces.config.ConfigurationException: java.util.concurrent.ExecutionException: com.sun.faces.config.ConfigurationException: Unable to parse document 'file:/C:/Users/axeli/Desktop/SeminarioPagina/build/web/WEB-INF/faces-config.xml': null
        at com.sun.faces.config.ConfigManager.getConfigDocuments(ConfigManager.java:761)
        at com.sun.faces.config.ConfigManager.initialize(ConfigManager.java:349)
        at com.sun.faces.config.ConfigureListener.contextInitialized(ConfigureListener.java:221)
        at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4736)
        at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5181)
        at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
        at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:725)
        at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:701)
        at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:717)
        at org.apache.catalina.startup.HostConfig.deployDescriptor(HostConfig.java:586)
        at org.apache.catalina.startup.HostConfig.deployApps(HostConfig.java:460)
        at org.apache.catalina.startup.HostConfig.check(HostConfig.java:1586)
        at sun.reflect.GeneratedMethodAccessor47.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:497)
        at org.apache.tomcat.util.modeler.BaseModelMBean.invoke(BaseModelMBean.java:300)
        at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.invoke(DefaultMBeanServerInterceptor.java:819)
        at com.sun.jmx.mbeanserver.JmxMBeanServer.invoke(JmxMBeanServer.java:801)
        at org.apache.catalina.manager.ManagerServlet.check(ManagerServlet.java:1460)
        at org.apache.catalina.manager.ManagerServlet.deploy(ManagerServlet.java:906)
        at org.apache.catalina.manager.ManagerServlet.doGet(ManagerServlet.java:344)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
        at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
        at org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:393)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
        at org.apache.catalina.filters.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:108)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
        at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:217)
        at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
        at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:614)
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142)
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
        at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616)
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518)
        at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091)
        at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:673)
        at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1500)
        at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1456)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
        at java.lang.Thread.run(Thread.java:745)
    Caused by: java.util.concurrent.ExecutionException: com.sun.faces.config.ConfigurationException: Unable to parse document 'file:/C:/Users/axeli/Desktop/SeminarioPagina/build/web/WEB-INF/faces-config.xml': null
        at java.util.concurrent.FutureTask.report(FutureTask.java:122)
        at java.util.concurrent.FutureTask.get(FutureTask.java:192)
        at com.sun.faces.config.ConfigManager.getConfigDocuments(ConfigManager.java:759)
        ... 49 more
    Caused by: com.sun.faces.config.ConfigurationException: Unable to parse document 'file:/C:/Users/axeli/Desktop/SeminarioPagina/build/web/WEB-INF/faces-config.xml': null
        at com.sun.faces.config.ConfigManager$ParseTask.call(ConfigManager.java:1012)
        at com.sun.faces.config.ConfigManager$ParseTask.call(ConfigManager.java:954)
        at java.util.concurrent.FutureTask.run(FutureTask.java:266)
        at com.sun.faces.config.ConfigManager.getConfigDocuments(ConfigManager.java:747)
        ... 49 more
    Caused by: java.lang.NullPointerException
        at com.sun.faces.config.ConfigManager$ParseTask.getDocument(ConfigManager.java:1172)
        at com.sun.faces.config.ConfigManager$ParseTask.call(ConfigManager.java:1003)
        ... 52 more

    28-Feb-2016 18:00:21.195 SEVERE [http-nio-8084-exec-10] org.apache.catalina.core.StandardContext.startInternal One or more listeners failed to start. Full details will be found in the appropriate container log file
    28-Feb-2016 18:00:21.195 SEVERE [http-nio-8084-exec-10] org.apache.catalina.core.StandardContext.startInternal Falló en arranque del Contexto [] debido a errores previos
    28-Feb-2016 18:00:21.227 SEVERE [http-nio-8084-exec-10] javax.faces.FactoryFinder$FactoryManager.copyInjectionProviderFromFacesContext Unable to obtain InjectionProvider from init time FacesContext. Does this container implement the Mojarra Injection SPI?
    28-Feb-2016 18:00:21.227 SEVERE [http-nio-8084-exec-10] javax.faces.FactoryFinder$FactoryManager.getFactory La aplicación no se ha inicializado correctamente durante el inicio, no se encuentra la fábrica: javax.faces.application.ApplicationFactory. Attempting to find backup.
    28-Feb-2016 18:00:21.227 SEVERE [http-nio-8084-exec-10] com.sun.faces.config.ConfigureListener.contextDestroyed Unexpected exception when attempting to tear down the Mojarra runtime
     java.lang.IllegalStateException: Could not find backup for factory javax.faces.application.ApplicationFactory. 
        at javax.faces.FactoryFinder$FactoryManager.getFactory(FactoryFinder.java:1135)
        at javax.faces.FactoryFinder.getFactory(FactoryFinder.java:379)
        at com.sun.faces.config.InitFacesContext.getApplication(InitFacesContext.java:142)
        at com.sun.faces.config.ConfigureListener.contextDestroyed(ConfigureListener.java:319)
        at org.apache.catalina.core.StandardContext.listenerStop(StandardContext.java:4783)
        at org.apache.catalina.core.StandardContext.stopInternal(StandardContext.java:5404)
        at org.apache.catalina.util.LifecycleBase.stop(LifecycleBase.java:232)
        at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:160)
        at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:725)
        at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:701)
        at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:717)
        at org.apache.catalina.startup.HostConfig.deployDescriptor(HostConfig.java:586)
        at org.apache.catalina.startup.HostConfig.deployApps(HostConfig.java:460)
        at org.apache.catalina.startup.HostConfig.check(HostConfig.java:1586)
        at sun.reflect.GeneratedMethodAccessor47.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:497)
        at org.apache.tomcat.util.modeler.BaseModelMBean.invoke(BaseModelMBean.java:300)
        at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.invoke(DefaultMBeanServerInterceptor.java:819)
        at com.sun.jmx.mbeanserver.JmxMBeanServer.invoke(JmxMBeanServer.java:801)
        at org.apache.catalina.manager.ManagerServlet.check(ManagerServlet.java:1460)
        at org.apache.catalina.manager.ManagerServlet.deploy(ManagerServlet.java:906)
        at org.apache.catalina.manager.ManagerServlet.doGet(ManagerServlet.java:344)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
        at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
        at org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:393)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
        at org.apache.catalina.filters.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:108)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
        at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:217)
        at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
        at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:614)
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142)
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
        at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616)
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518)
        at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091)
        at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:673)
        at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1500)
        at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1456)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
        at java.lang.Thread.run(Thread.java:745)

    28-Feb-2016 18:00:21.358 SEVERE [http-nio-8084-exec-10] javax.faces.FactoryFinder.releaseFactories Unable to call @PreDestroy annotated methods because no InjectionProvider can be found. Does this container implement the Mojarra Injection SPI?
    28-Feb-2016 18:00:21.390 INFO [http-nio-8084-exec-10] org.apache.catalina.startup.HostConfig.deployDescriptor Deployment of configuration descriptor C:\Users\axeli\AppData\Roaming\NetBeans\8.1\apache-tomcat-8.0.27.0_base\conf\Catalina\localhost\ROOT.xml has finished in 1.512 ms
And these are the libraries I am using right now:
Solution
java.lang.NullPointerException at com.sun.faces.config.ConfigManager$ParseTask.getDocument(ConfigManager.java:1172)
This usually only happens when there's a XML syntax error in the faces-config.xml itself and the XML parser (incorrectly) didn't throw an exception but just returned null. Pay carefully attention to the XML wellformedness of the document. I.e. every <element> must have a matching </element> and every " must have a matching ", etc.
If you're using an IDE make sure it has the necessary JSF / Java EE plugins which usually take care of XML validation. Or if you already have, pay attention to errors/warnings in IDE. In case you're unsure, copypaste the faces-config.xml in some online XML validation tool, such as http://www.xmlvalidation.com.