https://github.com/Yoast/wordpress-seo/issues/5296 https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=730094 https://stackoverflow.com/questions/25232975/php-filter-inputinput-server-request-method-returns-null I just wasted about 3 hours of my life due to this bug. It still exists even on PHP 7. I hope other people who have this issue can find my post, instead of slowly going insane like I did.