Ungroup all from selection

Hello:) i was trying to find something which will help me to Ungroup everything from selection to be able to add it on Action. I cant use normal ungroup becuase if i use it few times (in case there is more groups in selection) then script is stopping becuase there are no groups. So i tried script like this:

var doc;

function getChildAll(obj) {
var childsArr = [];
for (var i = 0; i < obj.pageItems.length; i++) {
childsArr.push(obj.pageItems[i]);
}
return childsArr;
}

function ungroupSelection() {
var selection = doc.selection;
for (var i = 0; i < selection.length; i++) {
var item = selection[i];
if (item.typename == "GroupItem") {
var elements = getChildAll(item);
for (var j = 0; j < elements.length; j++) {
elements[j].moveBefore(item);
}
item.remove();
ungroupSelection(); // Recursively ungroup newly ungrouped items
}
}
}

if (app.activeDocument) {
doc = app.activeDocument;
if (doc.selection.length > 0) {
ungroupSelection();
} else {
alert("Please make a selection before running this script.");
}
} else {
alert("Please open a document before running this script.");
}


Script is working but its showing me error like in attachment. How i can avoid it? or maybe there is some easier way to ungroup everything from selection?