Hello,
We are going to check the undefined index. As a workaround please add @ when you invoke replaceChartData to hide the notice:
@$docxx->replaceChartData($source, $target, $data);
Although this isn't a good practice, it will avoid the notice (and other errors that the method may show as well, so please use it carefully and only in this line until a new package is released).
Laravel (as Symfony and other PHP frameworks) throws an exception in the dev environment when a notice is thrown. You can avoid it changing the default configuration, but we are going to check and fix the undefined index notice.
Regards.