Overloading package functions

I want to overload a function in PL/SQL package wich returns

1.) 0 or SQLCODE on error and free (not existing) object name as output parameter
2.) free object name or NULL on error

The package is compiled successfully but when I call function I get PLS-00307 error (too many declarations of func_name match this call.

Should I declare overloading in some way and if yes, how?

declaration in packagespec:

    FUNCTION TMP_OBJECT_NAME
(object_name OUT VARCHAR2, prefix IN VARCHAR2 := '') RETURN NUMBER;

    FUNCTION TMP_OBJECT_NAME
(prefix IN VARCHAR2 := '') RETURN VARCHAR2;

package body code:

FUNCTION TMP_OBJECT_NAME(object_name OUT VARCHAR2, prefix IN VARCHAR2 := '')

    RETURN NUMBER IS     i_ret NUMBER;
    v_name USER_OBJECTS.OBJECT_NAME%TYPE; BEGIN
    i_ret := priv_TMP_OBJECT_NAME(v_name, prefix);     if i_ret = 0 then

        object_name := v_name;
    end if;
    RETURN i_ret;
EXCEPTION
   WHEN OTHERS THEN RETURN SQLCODE;
END; FUNCTION TMP_OBJECT_NAME(prefix IN VARCHAR2 := '')

    RETURN VARCHAR2 IS     i_ret NUMBER;
    v_name USER_OBJECTS.OBJECT_NAME%TYPE; BEGIN
    i_ret := priv_TMP_OBJECT_NAME(v_name, prefix);     if i_ret = 0 then

        RETURN v_name;
    else

        RETURN NULL;
    end if;
EXCEPTION
   WHEN OTHERS THEN RETURN NULL;
END;

--
Rastko Potocnik
rastko.potocnik_at_rtvslo.si