ap_vendor_pub_pkg.update_vendor_site_public will not set attribute6 to NULL

I have a long script and one section of it call ap_vendor_pub_pkg.update_vendor_site_public to set attribute5 and attribute6. Attribute6 has a value in it but needs to be set to null. The code executes successfully and does not return an error. However, when I query ap_supplier_sites_all, the attribute6 still has the original value in it and is not null. How do I set the attribute to null?

Thanks,

Nancy

Here is the section of the code:

DBMS_OUTPUT.PUT_LINE('Updating Supplier site attribute5 and attribute6');

DBMS_OUTPUT.PUT_LINE('attribute5 = '||j.attribute5);