new Functions blank Page after CI-Update

When you've got a blank screen and nothing is reported or logged, probably a fragment of code has a syntax error, PHP parsing fails. It might be your code or if you use packages added with Composer it might be there. When I am out of options of guessing where the error might be I use a very simple trick. Starting from the file index.php I follow code and put temporarily the line
echo '!!!'; exit;
When this output is seen, the code works to this point. Move this line down and refresh the page and so on till the moment the output disappears. Thus you can locate the problematic piece of code.

This is a very rudimentary trick, but for testing directly on the server when you start a new site it might be the only choice sometimes.