Ignore duplicate subscriptions.

    function extract(data, next) {

        var subscriptions = [];

        // to check for duplicate subscriptions

        var uniqueMap = {};

        data.mongo_subscriptions.forEach(function(s) {

            // There's one particular user who's ID doesn't exist in Sencha Forum DB.

            // Though... I was able to find a user with the same e-mail address,

            // but I think it's safer to just delete subscriptions of that user.

            if (s.userId !== 462980) {

                subscriptions.push({

                var r = {

                    user_id: data.usersMapByExternalId[s.userId].id,

                    target_id: data.targetsMap[TargetsTable.buildKey(s)].id,

                    created_at: DEFAULT_DATE

                });

                };

                // ignore duplicate subscriptions

                if (!uniqueMap[r.user_id+"-"+r.target_id]) {

                    subscriptions.push(r);

                }

                uniqueMap[r.user_id+"-"+r.target_id] = true;

            }

        });