[REG 5.10 => dev] Integer initialised in for loop is null after loop finishes

import QtQuick 2.5
import QtQuick.Controls 2.3

ApplicationWindow {
    visible: true
    width: 640
    height: 480

    Component.onCompleted: {
        var str = "ab";
        for (var inputIndex in str) {
            // ..
        }

        print(inputIndex)
    }
}