DSL expander can't add a field constraint to a fact when a previous field constraint has parentheses

I have made a little example to reproduce the problem.

Let us assume we have a very simple Wine class...
public class Wine {
private int age;
private String type;
private String country;
private String vineyard;
....

I define the following in my DSL:

[condition][]Il existe un vin "

: Wine()
[condition][]- plus vieux que "

[condition][]- du crû "

"

In the following rule, I can't add the last field constraint when the age of the prvious one is
"($y + 10)"

rule "Very Old Wine"

when
#conditions

1. there is a wine 10 years older than a person
   > Person($y : age)
   Il existe un vin "$v"

• plus vieux que "($y + 10)"

1. - plus vieux que "$y"

• du crû "Nuits-Saint-Georges"
  then
  #actions

End