Bug 1553413 - Update and harden form data filtering for privacy to account for no data being passed in. r=dao

Differential Revision: https://phabricator.services.mozilla.com/D32116

--HG--
extra : moz-landing-system : lando

toolkit/modules/sessionstore/PrivacyFilter.jsm

@@ -46,7 +46,7 @@ var PrivacyFilter = Object.freeze({
     // If the given form data object has an associated URL that we are not
     // allowed to store data for, bail out. We explicitly discard data for any
     // children as well even if storing data for those frames would be allowed.
-    if (data.url && !PrivacyLevel.check(data.url)) {
+    if (!data || (data.url && !PrivacyLevel.check(data.url))) {
       return null;
     }