You are populating items with the mailabs function (which is just one of several, plus you can if needs be write your own if your files/data are in a different structure) Using a suitable one is what the comment there is drawing attention to.
Are you sure that your files are in a format/directory structure that matches?
I’ve seen several cases where people set up their data in the structure for LJSpeech.
I’d suggest you Google both M-AI-Labs and LJSpeech to figure out if your structure matches them (or is some other structure) and make changes as appropriate, until the number of files is non-zero (ie that they’ve all been loaded correctly)