How to delete or remove a user attribute value

How I can remove/reset value of a user attribute to nothing.

I tried the below commands, but it failed

         If l_initials Is Not null Then

              l_emp_Vals(1)  := l_initials ;

             DBMS_LDAP.populate_mod_array(l_emp_array,DBMS_LDAP.MOD_REPLACE,'initials',l_emp_vals);

           Else

              l_emp_Vals(1) := null;

              DBMS_LDAP.populate_mod_array(l_emp_array,DBMS_LDAP.MOD_REPLACE,'initials',l_emp_vals);

           End If;

but it failed with following error message

Error Message : ORA-31202: DBMS_LDAP: LDAP client/server error: Invalid syntax.

00000057: LdapErr: DSID-0C090CBE, comment: Error in attribute conversion

operation, data 0, v23f0