xml - ORA-01084: invalid argument in OCI call -

i'm getting "ora-01084: invalid argument in oci call" error when i'm passing string.empty or "" input parameter of below stored procedure through vb.net code.

 create or replace procedure  sp_name     (       in_xml in clob,     )         begin select  xml.id,         xml.name         xmltable         ('root/child' passing xmltype(in_xml)             columns         id number path 'id',         name varchar2(50)path 'name') xml      exception when no_data_found null;         when others raise_application_error (-20999, 'sp_name'||sqlcode||'-'||sqlerrm) ;     end sp_name; 

below code used call sp.

    public class dal     private _db microsoft.practices.enterpriselibrary.data.database     dim param(0) object     param(0) = string.empty     _db.executenonquery(sp_name, param)     end class 

ps. i've specific scenario need pass empty string stored procedure.