Uncaught TypeError: Cannot read property 'innerHTML' of null (solution)

Recently I develop some static pages and got few pages Uncaught TypeError: Cannot read property 'innerHTML' of null or similar kind of issues.
Issues coming when something missing like classes, selector in some pages but we are calling each portion of JavaScript to perform all the pages.

 <h2 class="">Hello World</h2>

    <script>
        let demo = document.querySelector('.demo')
        console.log(demo.innerHTML)

    </script>

issues coming when I am calling demo class but there are no demo class in Dom. So, in this moment javascript throwing TypeError.

but, if we make it short with just logical operators && it's not giving any TypeError. For example,

let demo = document.querySelector('.demo')
        demo&&(
            console.log(demo.innerHTML)
        )

Thanks.