Issue 3448 - TypeError: this.treeElement is null error when closing Filter Preferences

chrome/content/ui/filters-filterview.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2015 Eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 615 matching lines @@
       this.data.splice(oldPosition, 1);
       this.data.splice(newPosition, 0, item);
       this.boxObject.invalidateRange(Math.min(oldPosition, newPosition), Math.max(oldPosition, newPosition));
     }
   },
 
   QueryInterface: XPCOMUtils.generateQI([Ci.nsITreeView]),
 
   setTree: function(boxObject)
   {
+    if (!boxObject)
+      return;
+
     this.init();
     this.boxObject = boxObject;
 
     if (this.boxObject)
     {
       this.noGroupDummy = {index: 0, filter: {text: this.boxObject.treeBody.getAttribute("noGroupText"), dummy: true}};
       this.noFiltersDummy = {index: 0, filter: {text: this.boxObject.treeBody.getAttribute("noFiltersText"), dummy: true}};
       this.editDummy = {filter: {text: ""}};
 
       let atomService = Cc["@mozilla.org/atom-service;1"].getService(Ci.nsIAtomService);
@@ skipping 188 matching lines @@
   getProgressMode: () => null,
   getImageSrc: () => null,
   isSeparator: () => false,
   performAction: () => {},
   performActionOnRow: () => {},
   performActionOnCell: () => {},
   getCellValue: () => null,
   setCellValue: () => {},
   selectionChanged: () => {}
 };