Fatal error: Uncaught TypeError: mysqli_query(): Argument #1 ($mysql) must be of type mysqli, null given in /home1/sdksolut/public_html/wbsdcb/to_inc/common.php:517 Stack trace: #0 /home1/sdksolut/public_html/wbsdcb/to_inc/common.php(517): mysqli_query(NULL, 'select date_for...') #1 /home1/sdksolut/public_html/wbsdcb/event.php(96): change_date__month_format('2019-08-04') #2 {main} thrown in /home1/sdksolut/public_html/wbsdcb/to_inc/common.php on line 517