SQL & PL/SQL :: Use Model Clause To Get Comma Separate Single Row For Multiple Rows?

I am trying to use model clause to get comma separate single row for multiple rows. My scenario is like this:

SQL> desc test1
Name Null? Type
----------------------------------------------------- -------- ------------------------------------
ID NUMBER
VALUE CHAR(6)

SQL> select * from test1 order by id;

ID VALUE
---------- ------
1 Value1
2 Value2
3 Value3
4 Value4
5 Value4
6
7 value5
8

The query that I have is:
SQL> with t as
2 ( select distinct substr(value,2) value
3 from test1
4 model
5 ignore nav
6 dimension by (id)
7 measures (cast(value as varchar2(100)) value)
8 rules
9 ( value[any] order by id = value[cv()-1] || ',' || value[cv()]
10 )
11 )
12 select max(value) oneline
13 from t;

ONELINE
---------------------------------------------------------------------------------------------------
Value1,Value2,Value3,Value4,Value4,,value5,

what I want is : null value should not come and duplicate value should not come (Value4 in output above)