Forms plsql library problem

Hi

I have a problem with custom plsql library attached to my form. Calling any library function from the form

gives me ORA-06503 PL/SQL Function returned without value. ORA-01403 no data found.

From the library pll file all I see in function body is:

function x (y in varchar2) return varchar2

  is

begin

  null;

end;

Can the code be wrapped? or how am I supposed to change it?

I dont think that its just NULL