Internal error

[ZiFQFyjM-QrdysH1f8A1hAAAAAs] /index.php?title=User:OWAFoster54&oldid=19491 Error from line 1573 of /usr/www/users/a9/pc/racismdefinitions.org/includes/page/Article.php: Call to a member function getTimestamp() on null

Backtrace:

#0 /usr/www/users/a9/pc/racismdefinitions.org/includes/page/Article.php(711): Article->setOldSubtitle()
#1 /usr/www/users/a9/pc/racismdefinitions.org/includes/actions/ViewAction.php(63): Article->view()
#2 /usr/www/users/a9/pc/racismdefinitions.org/includes/MediaWiki.php(511): ViewAction->show()
#3 /usr/www/users/a9/pc/racismdefinitions.org/includes/MediaWiki.php(302): MediaWiki->performAction()
#4 /usr/www/users/a9/pc/racismdefinitions.org/includes/MediaWiki.php(900): MediaWiki->performRequest()
#5 /usr/www/users/a9/pc/racismdefinitions.org/includes/MediaWiki.php(527): MediaWiki->main()
#6 /usr/www/users/a9/pc/racismdefinitions.org/index.php(44): MediaWiki->run()
#7 {main}