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/art.php(436): art::call() #5 /home/nfo/prog/a/art.php(469): art::callout() #6 /home/nfo/prog/a/mod.php(188): art::read() #7 /home/nfo/prog/a/mod.php(141): mod::build() #8 /home/nfo/prog/a/mod.php(148): mod::block() #9 /home/nfo/prog/sys.php(38): mod::blocks() #10 /home/nfo/index.php(14): require('...') #11 {main} thrown in /home/nfo/prog/a/art.php on line 45