SQL & PL/SQL

Hi there

I'm using mod plsql to update a database tabe from an html form. The form has a matrix of checkboxes which I'm passing into a procedure as varchar2 table types. The problem I get is that it gives me an error if one of the check boxes on a row is null (NON-DEFAULT VARIABLES IN PROCEDURE NOT IN FORM) as it's not passing anything for that parameter in the procedure. My procedure is defined as:

PROCEDURE add_items (in_article_id IN NUMBER DEFAULT NULL
,in_related_id IN varchar2_table
,in_relate IN varchar2_table
,in_section IN varchar2_table
,in_preview IN varchar2_table
,in_session_id IN NUMBER) IS

where in_relate , in_section and in_preview are the parameters that the check boxes relate to. My form has the following inputs:

<FORM name="related_results" action="ce_related.add_items_table" method="post">
<input name="in_article_id" type="hidden" value="'||in_article_id||'">
<INPUT type=hidden name="in_session_id" value="'||in_session_id||'">
<input name="in_related_id" type="hidden" value="'||v_article.article_id||'">
<input name="in_relate" value="1" type="checkbox">
<input name="in_section" value="6" type="checkbox">

I have tried adding a 'DEFAULT NULL' clause to the procedure parameter, but this gives the error 'Error(356,62): PLS-00382: expression is of wrong type'. I have also tried using the owa_util.ident_arr datatype, but this doesn't work either. Has anyone got any ideas?

Cheers, Kate