I am seeing this error

Uncaught TypeError: Cannot read properties of null (reading 'parentElement') at (index):15 at Array.forEach () at IntersectionObserver. ((index):12)

Here is the code:

<script>window.addEventListener('DOMContentLoaded', () => {

    const observer = new IntersectionObserver(entries => {
        entries.forEach(entry => {
            const id = entry.target.getAttribute('id');
            if (entry.intersectionRatio > 0) {
                document.querySelector(`nav li a[href="#${id}"]`).parentElement.classList.add('active');
            } else {
                document.querySelector(`nav li a[href="#${id}"]`).parentElement.classList.remove('active');
            }
        });
    });

    
    document.querySelectorAll('div[id]').forEach((div) => {
        observer.observe(div);
    });
    
});
</script>

Script is working well, but seeing errors in the console. Kindly let me know what to do.