html – Undefined index: module error in php


ecently I have made a form code and attached modules to it. but soon after I have reached an error saying
Notice: Undefined index: module in F:websitewebpagegate.php on line 68

here is the line that was mentioned

`switch ($_GET("module")) {
case "settings":
    include('settings.php');
    break;
default:
 break;}`

I am also mentioning the code in the that I showed up ib the link

<a class="nav-link" href="gate.php?module=settings"> Settings </a> please rectify this error for me and sorry for any in trouble.