urlreferrer returned null in webview android

I have a web application which is a mobile website, the same website works independently and inside a android app also.

Due to certain regulations to avoid cyber crimes/hacks, we are instructed to check the urlreferrer at each page load. When working in a web browser, it works as desired, I get proper values in the urlreferrer, but when I open the same pages in android app, it always returns null value in the urlreferrer. Due to which the program treats it as a hack attack and redirects it to error or session expired page.

Does anyone have any idea about this? Can any one please guide me what may be going wrong?