check if possible parent exists before checking if it contains another element

www/common/treesome.js

@@ -96,7 +96,7 @@ define([], function () {
 
     // not being used internally, but is useful externally
     tree.contains = function (el, root) {
-        return el && root.contains && root.contains(el);
+        return el && root && root.contains && root.contains(el);
     };
 
     var siblingCount = tree.siblingCount = function (el) {