GUIDE custom CloseRequestFcn receives empty handles

Good Day I tried now for mutliple hours to resolve the following issue:

I want to call a custom function when the user clicks on the 'x' button on the top right corner of the window (tries to close the window).

I have a cancel button which should do the same thing, and it works without a problem. But if i try to overrite the CloseRequestFcn in the following way:

set(handles.figure1,'CloseRequestFcn',{@my_CloseRequest, handles});

which I put in the xxx_OpeningFcn, i have the problem, that the passed handles are empty. My custom close function looks like this:

function my_CloseRequest(hObject, eventdata, handles) 
xxx_OutputFcn(hObject, eventdata, data);

What am i missing? why does it work with my cancel button but not with the custom my_CloseRequest? Why are the handles deleted or not accessible? Is there any workaround?

I am using a mac, could this have anything to do with it?

Thank you for any help