Accessibility issue with opening galleries in lightbox

Hi
When using your lightbox feature in WordPress galleries, WAVE is giving me the following accessibility error, “Empty Button – a button is empty or has no value”. The lightbox’s close, next, and previous buttons are causing this; I’ve tried to add alt text as well as a value using jquery in the footer but cannot seem to get it right to fix the error. Is there a possibility that you can share how to fix this, or correct it in the next update?
Thanks,

The page I need help with: [log in to see the link]