Script has an Error Pop up and I don't know why

Good Morning,

I have a script I wrote that uses Radio Buttons to select which function to use.  It works as intended however when the "Extra Artboards" button is selected there is an Error that Pops up and I don't know why.

Thank you for your time!!

var choice
var w = new Window("dialog");
var g = w.add("group");
var a = g.add("radiobutton", undefined, "Main Artboard");
var b = g.add("radiobutton", undefined, "Extra Artboards");
var button = w.add("button", undefined, "OK");
var radiobuttons = [a, b];
for (var i = 0; i < radiobuttons.length; i++) {
    (function (i) {
        radiobuttons[i].onClick = function () {
            choice = radiobuttons[i].text;
        };
    })(i);
}
w.show();

var removeArtboards;
if (choice == "Main Artboard") {
    // Main
    function removeArtboards ( arr ) {
        var i = arr.length; while ( i-- ) activeDocument.artboards[ arr[i] ].remove();  
    } 
    removeArtboards( [0] );

} else if (choice == "Extra Artboards") {
    // Extra
    function removeArtboards() {
        var doc = app.activeDocument;
        var artboardsLength = doc.artboards.length
        for (var i = artboardsLength - 1; i >= 0; i--) {
            if (app.activeDocument.artboards[i].name != 'Artboard 1') {
                activeDocument.artboards[i].remove();
            }
        }
    }
    removeArtboards();
}