CloudCode getSessionToken() doesn't work anymore

Question

I'm facing a strange problem. The follow code worked until a few weeks ago. Do you know why now the session token that I get is always undefined?

Thanks in advance!

Carmelo

Parse.Cloud.define("UserSessionTokenWithFacebookId", function(request, response) {

   Parse.Cloud.useMasterKey();

   var userQuery = new Parse.Query(Parse.User);
   userQuery.equalTo("facebookID", request.params.facebookID);
   userQuery.first({
      success:function(user) {

           console.log("sessionToken: " + user.getSessionToken());

           response.success(user.getSessionToken());
      },
      error:function(_error) {

           response.error("User failed");
           console.log("Error fetching user: " + _error.code);
      }
   });
})