下面是我的jsp页面的代码部分，当我打印时，rs.getString（1）打印完美但是只要我把rs.getString（1）放在if块中就会显示空指针异常。请帮忙
String nam=request.getParameter("n");
String query = "select name from ques where username='"+userid+"'";
Statement st=con.prepareStatement(query);
ResultSet rs = st.executeQuery(query);
while(rs.next()){
out.println(rs.getString(1));
if(rs.getString(1).equals(nam)){
out.print("hello");
}
}