Fatal error– failed to open stream — Missing the file referred to

I’d neglected my site for a while. I don’t remember what I was last in th emiddle of when I left it; but I’ve returned to find:

Warning: require(/home/mysite.com/htdocs/wp-includes/class-wp-paused-extensions-storage.php): failed to open stream: No such file or directory in /home/mysite.com/htdocs/wp-settings.php on line 20

Fatal error: require(): Failed opening required ‘/home/mysite.com/htdocs/wp-includes/class-wp-paused-extensions-storage.php’ (include_path=’.:/usr/share/pear/’) in /home/mysite.com/htdocs/wp-settings.php on line 20

The file class-wp-paused-extensions-storage.php doesn’t seem to exist.

Have you got ideas how to get the site accessible again?