请问这句话为什么总是弹出错误，但是我是按照老师的说法写的啊
String charset = config.getInitParameter("charset");
String nofilter = config.getInitParameter("nofilter");
这两句话这里
严重: Servlet.service() for servlet jsp threw exception
java.lang.NullPointerException
at com.kai.FilterFirst.First.doFilter(First.java:32)
<filter>
<display-name>firstfilter</display-name>
<filter-name>firstfilter</filter-name>
<filter-class>com.kai.FilterFirst.First</filter-class>
<init-param>
<param-name>nofilter</param-name>
<param-value>index;fail;/servlet/login</param-value>
</init-param>
<init-param>
<param-name>charset</param-name>
<param-value>UTF-8</param-value>
</init-param>
</filter>
