问date_format要求参数%1为DateTimeInterface/致命错误:调用中布尔值的成员函数add()

EN

<?php
include "dbConnect.php";
function getTimeTable($tutorID, $parseDate) {
    //'$parseDate'
    global $con;
    $today = date ( "Y-m-d" );
    $time_table_res = mysqli_query ( $con, "SELECT BeginTime, EndTime FROM TimeTable WHERE TutorId = '$tutorID'" );
    $timetable = array ();
    $num_rows = mysqli_num_rows ( $time_table_res );

    if ($num_rows > 0) {
        while ( $row = mysqli_fetch_array ( $time_table_res, MYSQLI_ASSOC ) ) {
            $begin_time = DateTime::createFromFormat ( 'Y-m-d g:i a', $parseDate . " " . $row ['BeginTime'] );
            $end_time = DateTime::createFromFormat ( 'Y-m-d g:i a', $parseDate . " " . $row ['EndTime'] );

             while ( $begin_time <= $end_time ) {

                $fdate = date_format($begin_time, 'g:i a'); 
                array_push ( $timetable, $fdate );
                $begin_time->add ( new DateInterval ( 'PT30M' ) );
            } 
        }
    }
    return $timetable;
}
?>