i am using the redy made paging tags.B But it give me a error of null pontinter exception. the first page is displayed correctly.But when i click next it gives the error

<%@ taglib uri="http://jsptags.com/tags/navigation/pager" prefix="pg" %> <%

Iterator i = null; Set tutorials = (Set ) request.getAttribute("tut_lst"); request.setAttribute("tut_lst",tutorials);

i = tutorials.iterator(); // error occus here

%>

<%

   while(i.hasNext())
   {
       Tutorials t = (Tutorials)i.next();

%>

        <BR> <a href ="down?tid=<%out.println(t.getUploadid() );%> ">        <%out.println(t.getFilename()); %> </a></td>

    </pg:item>

<%

      }

%>

<pg:first>
  <a href="<%= pageUrl %>">[ (<%= pageNumber %>) |&lt; Previous ]</a>
</pg:first>

<pg:prev>
  <a href="<%= pageUrl %>">[ (<%= pageNumber %>) &lt;&lt; Previous ]</a>
</pg:prev>

<pg:pages>
   <a href="<%= pageUrl %>"><%= pageNumber %></a>
</pg:pages>

<pg:next>
  <a href="<%= pageUrl %>">[ Next &gt;&gt; (<%= pageNumber %>) ]</a>
</pg:next>

<pg:last>
  <a href="<%= pageUrl %>">[ Last &gt;| (<%= pageNumber %>) ]</a>
</pg:last>