in api/Serialization.ts [332:346]
    var _extend = function(out) {
        out = out || {};
        for (var i = 1; i < arguments.length; i++) {
            if (!arguments[i])
                continue;
            for (var key in arguments[i]) {
                if (arguments[i].hasOwnProperty(key))
                    out[key] = arguments[i][key];
            }
        }
        return out;
    };