fixed problem with empty student list for therapists

sails/src/api/models/Supervisor.js

@@ -275,6 +275,8 @@ module.exports = {
           .catch(function (err) {
           .catch(function (err) {
             callback(err, l);
             callback(err, l);
           });
           });
+       } else {
+	callback(err, l);
        }
        }
       }); // end async.eachSeries
       }); // end async.eachSeries
     })
     })