为什么我上传的时候 报错，导入老师的代码运行也一样

java.lang.NullPointerException: charsetName

at java.lang.String.<init>(String.java:442)

at com.jspsmart.upload.SmartUpload.upload(SmartUpload.java:234)

at com.imooc.servlet.SmartUploadServlet.doPost(SmartUploadServlet.java:44)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:646)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)

at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)

at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)

at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:503)

at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)

at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)

at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)

at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)

at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:421)

at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1070)

at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:611)

at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.doRun(AprEndpoint.java:2466)

at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.run(AprEndpoint.java:2455)

at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)

at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)

at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)

at java.lang.Thread.run(Thread.java:619)