404-page with Tracking-code and Empty referer adress

Dear All
on my HP i released a 404- Page incl. tracking-code like written in FAQ

◦Add the Piwik tracking code in this custom 404 page. In the Javascript tracking code, add the following:
piwikTracker.setDocumentTitle('404/URL = '+String(document.location.pathname+document.location.search).replace(///g,"%2f") + '/From = ’ + String(document.referrer).replace(///g,"%2f"));
after the line
var piwikTracker = Piwik.getTracker(…)
and before the line piwikTracker.trackPageView();

On " Pages Titles" i see 404 entries but the referer is empty
like below

URL = /content/fehler404.html
From =

can pls somebody help me to solve the problem ?

Nice Day and BR
Willi Kluter