upload sshkey file meets null

[ShiYour]

when I upload a sshkey , I choose the file '/DICE/Uploads/1490698512629test'. after submit, the backend says file == null

[ShiYour]

警告: java.lang.NullPointerException
javax.el.ELException: java.lang.NullPointerException
at org.apache.el.parser.AstValue.invoke(AstValue.java:292)
at org.apache.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:273)
at javax.faces.event.MethodExpressionActionListener.processAction(Unknown Source)
at javax.faces.event.ActionEvent.processListener(Unknown Source)
at javax.faces.component.UIComponentBase.broadcast(Unknown Source)
at javax.faces.component.UICommand.broadcast(Unknown Source)
at javax.faces.component.UIViewRoot.broadcastEvents(Unknown Source)
at javax.faces.component.UIViewRoot.processApplication(Unknown Source)
at com.sun.faces.lifecycle.InvokeApplicationPhase.execute(Unknown Source)
at com.sun.faces.lifecycle.Phase.doPhase(Unknown Source)
at com.sun.faces.lifecycle.LifecycleImpl.execute(Unknown Source)
at javax.faces.webapp.FacesServlet.service(Unknown Source)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:110)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:506)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:169)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:962)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:445)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1115)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:637)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:318)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.NullPointerException
at com.utility.Uploader.upload(Uploader.java:14)
at com.basic.CpuView.upload(CpuView.java:95)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.apache.el.parser.AstValue.invoke(AstValue.java:279)
... 31 more