minor update for finding tutorial

Author: tienbku

app/controllers/tutorial.controller.js

@@ -55,7 +55,13 @@ exports.findOne = (req, res) => {
 
   Tutorial.findByPk(id)
     .then(data => {
-      res.send(data);
+      if (data) {
+        res.send(data);
+      } else {
+        res.status(404).send({
+          message: `Cannot find Tutorial with id=${id}.`
+        });
+      }
     })
     .catch(err => {
       res.status(500).send({