title: Database in Postman returning 'Null'. It is not returning my newly added data
body: <p>I want to create a book API. With the very basic 'post' command I'm trying to add a new book to the database. But when I return it postman shows me the already added books in the database. And returning 'null' instead of my newly added book.</p>
  <p>Here's the code: (To add a new Book)</p>
  <pre><code>app.post(&quot;/book&quot;, (req,res) =&gt; {
      const {newBook} = req.body;
      db.books.push(newBook);
      return res.json(db.books);
  })
  </code></pre>
  <p><a href="https://i.stack.imgur.com/uaqhQ.png" rel="nofollow noreferrer">enter image description here</a></p>