title: Error java.lang.NullPointerException JSF
body: <p>I'm using jsf/primefaces, I'm getting this npe, I'm invoking a method "registrar" from a form but appears that I'm doing it wrong.
  I have the class ProfesorBean.java and the view edicion.xhtml</p>
  
  <pre><code>**Class: ProfesorBean**
  ...............................................
  
  @ManagedBean(name="profesorBean")
  @SessionScoped
  
  public class ProfesorBean {
      private Profesor profesor;
      private List&lt;Profesor&gt; profesores;
      private Integer autogenerado=2;
  
  public String registrar(){
      if (profesor.getCodigo()!=null) {             
      }else {
          profesor.setCodigo(autogenerado);
          profesores.add(profesor);
          autogenerado++;
      }
      profesor=null;
      return "listado";
  }
  
  }
  ...............................................
  </code></pre>
  
  <p>Here is the part of form that is submitted edicion.xhtml</p>
  
  <pre><code>...............................................
  &lt;f:facet name="footer"&gt;
                          &lt;p:commandButton value="#{msjs.form_boton_registrar}" 
                                           action="#{profesorBean.registrar}"
                                           update="@form"
                                           ajax="false"
                                          /&gt;
                          &lt;p:commandButton value="#{msjs.form_boton_limpiar}" 
                                           update="panel" 
                                           process="@this"  &gt;
                              &lt;p:resetInput target="panel" /&gt;
                          &lt;/p:commandButton&gt;
                          &lt;p:commandButton  action="listado"
                                           value="#{msjs.form_boton_regresar}"
                                           process="@this"
                                           immediate="true"
                                           ajax="false"/&gt;
                      &lt;/f:facet&gt;
  </code></pre>
  
  <p>Here is the error</p>
  
  <pre><code>FATAL:   JSF1073: se ha interceptado javax.faces.FacesException durante el procesamiento de INVOKE_APPLICATION 5 : UIComponent-ClientId=, Mensaje=#{profesorBean.registrar}: java.lang.NullPointerException
  FATAL:   #{profesorBean.registrar}: java.lang.NullPointerException
  javax.faces.FacesException: #{profesorBean.registrar}: java.lang.NullPointerException
  at com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:89)
  at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
  at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:198)
  at javax.faces.webapp.FacesServlet.service(FacesServlet.java:646)
  at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1682)
  at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:318)
  at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:160)
  at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:734)
  at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:673)
  at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:99)
  at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:174)
  at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:357)
  at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:260)
  at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:188)
  at org.glassfish.grizzly.http.server.HttpHandler.runService(HttpHandler.java:191)
  at org.glassfish.grizzly.http.server.HttpHandler.doHandle(HttpHandler.java:168)
  at org.glassfish.grizzly.http.server.HttpServerFilter.handleRead(HttpServerFilter.java:189)
  at org.glassfish.grizzly.filterchain.ExecutorResolver$9.execute(ExecutorResolver.java:119)
  at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter(DefaultFilterChain.java:288)
  at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:206)
  at org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:136)
  at org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:114)
  at org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:77)
  at org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:838)
  at org.glassfish.grizzly.strategies.AbstractIOStrategy.fireIOEvent(AbstractIOStrategy.java:113)
  at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.run0(WorkerThreadIOStrategy.java:115)
  at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:55)
  at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:135)
  at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:564)
  at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:544)
  at java.lang.Thread.run(Thread.java:745)
  
  Caused by: javax.faces.FacesException: #{profesorBean.registrar}: java.lang.NullPointerException
  at com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:118)
  at javax.faces.component.UICommand.broadcast(UICommand.java:315)
  at javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:790)
  at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:1282)
  at com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:81)
  ... 30 more
  
  Caused by: javax.faces.el.EvaluationException: java.lang.NullPointerException
  at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:101)
  at com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:102)
  ... 34 more
  
  Caused by: java.lang.NullPointerException
  at pe.edu.cibertec.managed.ProfesorBean.registrar(ProfesorBean.java:56)
  at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
  at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
  at java.lang.reflect.Method.invoke(Method.java:483)
  at com.sun.el.parser.AstValue.invoke(AstValue.java:275)
  at com.sun.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:304)
  at com.sun.faces.facelets.el.TagMethodExpression.invoke(TagMethodExpression.java:105)
  at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:87)
  ... 35 more
  </code></pre>