在测试项目源码的时候注册模块总是不成功，原因为提交注册后在调用UserDao类中的getUserByName(String name)这个方法时，不能正确拿到SessionFactoryProvider类提供的session对象，报空指针异常，但检查SessionFactoryProvider类后没发现错误，请问是什么原因造成的？谢谢

严重: Servlet.service() for servlet UserServlet threw exception
java.lang.NullPointerException
at com.soft.dao.UserDao.getUserByName(UserDao.java:173)
at com.soft.service.UserServlet.checkName(UserServlet.java:165)
at com.soft.service.UserServlet.doPost(UserServlet.java:44)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.soft.service.CharactorFilter.doFilter(CharactorFilter.java:35)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:286)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:845)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
at java.lang.Thread.run(Thread.java:619)