filter out null prev_feed upon startup

init.js

@@ -8,14 +8,15 @@ require(['dojo/_base/kernel', 'dojo/ready'], function (dojo, ready) {
 			const toolbar = document.forms["toolbar-main"];
 			const order_by = dijit.getEnclosingWidget(toolbar.order_by);
 			const view_mode = dijit.getEnclosingWidget(toolbar.view_mode);
-			
-			prev_prefs = {
-				order_by: order_by.attr("value"),
-				view_mode: view_mode.attr("value"),
-			};
-			prev_key = "ttrss:feedprefs:"+prev_feed;
-			localStorage.setItem(prev_key, JSON.stringify(prev_prefs));
 
+			if (this.prev_feed != null) {
+				prev_prefs = {
+					order_by: order_by.attr("value"),
+					view_mode: view_mode.attr("value"),
+				};
+				prev_key = "ttrss:feedprefs:"+this.prev_feed;
+				localStorage.setItem(prev_key, JSON.stringify(this.prev_prefs));
+			}
 			this.prev_feed = feed[0];
 
 			key = "ttrss:feedprefs:"+feed[0];