菜鸟求助

exception org.apache.jasper.JasperException: An exception occurred processing JSP page /index.jsp at line 63: <%@page import="java.util.*"%>
4: <%@page import="com.wy.domain.GoodsForm" %>
5: <jsp:useBean id="newGood" scope="page" class="com.wy.dao.GoodsDao"/>
6: <%List nowList =newGood.selectMark(Integer.valueOf("0"));%>
7: <%List freeList =newGood.selectMark(Integer.valueOf("1"));%>
8: <html>
9: <head>
Stacktrace:
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:510)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:419)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
root cause java.lang.NullPointerException
com.wy.dao.GoodsDao.selectMark(GoodsDao.java:52)
org.apache.jsp.index_jsp._jspService(index_jsp.java:70)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:377)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
求高手指点..0.0本人完全菜鸟.