麻烦老师帮我看下，为什么是空指针呢？

package com.imooc.sm.global;

import com.imooc.sm.entity.Log;
import com.imooc.sm.entity.Staff;
import com.imooc.sm.service.LogService;
import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.annotation.After;
import org.aspectj.lang.annotation.AfterThrowing;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;

@Component
@Aspect
public class LogAdvice {
   @Autowired
   private LogService logService;

   @After("execution(* com.imooc.sm.controller.*.*(..)) && !execution(* com.imooc.sm.controller.SelfController.*(..))")
   public void operationLog(JoinPoint joinPoint) {
       Log log = new Log();
       log.setMoudle(joinPoint.getTarget().getClass().getSimpleName());
       log.setOperation(joinPoint.getSignature().getName());
       HttpServletRequest request = (HttpServletRequest) joinPoint.getArgs()[0];
       HttpSession session = request.getSession();
       Object obj = session.getAttribute("USER");
       Staff staff = (Staff) obj;
       log.setOperator(staff.getAccount());
       log.setResult("成功");

       logService.addOperationLog(log);

   }

   @AfterThrowing(throwing = "e", pointcut = "execution(* com.imooc.sm.controller.*.*(..))")
   public void systemLog(JoinPoint joinPoint, Throwable e) {
       Log log = new Log();
       log.setMoudle(joinPoint.getTarget().getClass().getSimpleName());
       log.setOperation(joinPoint.getSignature().getName());
       HttpServletRequest request = (HttpServletRequest) joinPoint.getArgs()[0];
       HttpSession session = request.getSession();
       Object obj = session.getAttribute("USER");
       Staff staff = (Staff) obj;
       log.setOperator(staff.getAccount());
       log.setResult(e.getClass().getSimpleName());
       logService.addSystemLog(log);
   }

   @After("execution(* com.imooc.sm.controller.SelfController.login(..))")
   public void loginLog(JoinPoint joinPoint) {
       Log log = new Log();
       log.setMoudle(joinPoint.getTarget().getClass().getSimpleName());
       log.setOperation(joinPoint.getSignature().getName());
       HttpServletRequest request = (HttpServletRequest) joinPoint.getArgs()[0];
       HttpSession session = request.getSession();
       Object obj = session.getAttribute("USER");
       if (obj == null) {
           log.setOperation(request.getParameter("account"));
           log.setResult("失败");
       } else {
           Staff staff = (Staff) obj;
           log.setOperator(staff.getAccount());
           log.setResult("成功");
       }
       logService.addLoginLog(log);
   }

   @Before("execution(* com.imooc.sm.controller.SelfController.logout(..))")
   public void logoutLog(JoinPoint joinPoint) {
       Log log = new Log();
       log.setMoudle(joinPoint.getTarget().getClass().getSimpleName());
       log.setOperation(joinPoint.getSignature().getName());
       HttpServletRequest request = (HttpServletRequest) joinPoint.getArgs()[0];
       HttpSession session = request.getSession();
       Object obj = session.getAttribute("USER");
       if (obj == null) {
           log.setOperation(request.getParameter("account"));
           log.setResult("失败");
       } else {
           Staff staff = (Staff) obj;
           log.setOperator(staff.getAccount());
           log.setResult("成功");
       }
       logService.addLoginLog(log);
   }
}
进不去个人中心哦