No attribute named is defined


I’m currently writing a test with gatling and i got an unresolved issue.
In the code below, i’m checking a dataz an saving it in the session :

http("Get user devoirs")
 .get(baseUrl + "/viescolaire/evaluations/devoirs?_=1486979226256")

But when i’m calling this :

http("Get competences devoir")
 .get(baseUrl + "/viescolaire/evaluations/competences/devoir/${idDevoir}?_=1486979226269")

Gatling report : > Failed to build request Get competences devoir: No attribute named ‘idDevoir’ is defined 1 (Infinity%).

After checking the session content, the session contains my key “idDevoir”. Can someone help me ?

Best regards,