Going to Special:Block with a username filled gives
[error] [6f820a4c2fffa2cd6e7b868f] /wiki/index.php/Special:Block/Newuser ErrorException from line 90 of /var/www/html/wiki/includes/libs/MapCacheLRU.php: PHP Warning: array_key_exists(): The first argument should be either a string or an integer [error] [6f820a4c2fffa2cd6e7b868f] /wiki/index.php/Special:Block/Newuser ErrorException from line 61 of /var/www/html/wiki/includes/libs/MapCacheLRU.php: PHP Warning: array_key_exists(): The first argument should be either a string or an integer [error] [6f820a4c2fffa2cd6e7b868f] /wiki/index.php/Special:Block/Newuser ErrorException from line 68 of /var/www/html/wiki/includes/libs/MapCacheLRU.php: PHP Warning: Illegal offset type
Happens on Wikimedia production as well:
28 Illegal offset type in /srv/mediawiki/php-1.27.0-wmf.21/includes/libs/MapCacheLRU.php on line 68 28 Array key should be either a string or an integer in /srv/mediawiki/php-1.27.0-wmf.21/includes/libs/MapCacheLRU.php on line 90 28 Array key should be either a string or an integer in /srv/mediawiki/php-1.27.0-wmf.21/includes/libs/MapCacheLRU.php on line 61