Warning: Undefined variable $rt in /home/nfo/prog/a/art.php on line 45

Fatal error: Uncaught TypeError: join(): If argument #1 ($separator) is of type string, argument #2 ($array) must be of type array, null given in /home/nfo/prog/a/art.php:45 Stack trace: #0 /home/nfo/prog/a/art.php(45): join() #1 /home/nfo/prog/a/art.php(257): art::btedit() #2 /home/nfo/prog/a/art.php(417): art::titles() #3 /home/nfo/prog/a/art.php(429): art::build() #4 /home/nfo/prog/a/api.php(291): art::call() #5 /home/nfo/prog/a/api.php(343): api::build() #6 /home/nfo/prog/a/api.php(323): api::callr() #7 /home/nfo/prog/a/api.php(336): api::load() #8 /home/nfo/prog/a/api.php(377): api::boot() #9 /home/nfo/prog/a/md.php(227): api::arts() #10 /home/nfo/prog/a/mod.php(211): md::cat_mod_j() #11 /home/nfo/prog/a/mod.php(132): mod::build() #12 /home/nfo/prog/a/mod.php(127): mod::block() #13 /home/nfo/prog/a/mod.php(148): mod::block() #14 /home/nfo/prog/sys.php(38): mod::blocks() #15 /home/nfo/index.php(14): require('...') #16 {main} thrown in /home/nfo/prog/a/art.php on line 45