PHP warning sp-core-functions.php on line 273

PHP Warning: array_key_exists(): The first argument should be either a string or an integer in D:\inetpub\vhosts\soccerside.net\httpdocs\wp-content\plugins\sportspress\includes\sp-core-functions.php on line 273

I am using the champion wordpress theme.
ORIGINAL : http://champion.stylemixthemes.com/calendar/fixtures/
MINE : http://soccerside.net/calendar/premier-league-fixtures/

Please help!

https://ww.wp.xz.cn/plugins/sportspress/