'length' of null

[Angee]

How can i solve this issue? anyone can help me ? I'm starting using Javascript
Error:   

 Uncaught TypeError: Cannot read property 'length' of null
    at HTMLInputElement.<anonymous> (hr_employee_form.php:678)
    at HTMLInputElement.dispatch (VM3361 jquery.js:3)
    at HTMLInputElement.r.handle (VM3361 jquery.js:3)

Code:
        let url_string = window.location.href;
        let url = new URL(url_string);                              
        let empid = url.searchParams.get("empid");