下面是错误代码，希望可以帮我解决下

type Exception report

message

description The server encountered an internal error () that prevented it from fulfilling this request.

exception

java.lang.NullPointerException
com.witbridge.ebook.action.CustomerAction.login(CustomerAction.java:23)
com.witbridge.ebook.servlet.Login.login(Login.java:36)
com.witbridge.ebook.servlet.Login.doPost(Login.java:28)
javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
com.witbridge.ebook.util.EncodingFilter.doFilter(EncodingFilter.java:23)


note The full stack trace of the root cause is available in the Apache Tomcat/6.0.30 logs.