public function getStart(): ?\DateTimeInterface
    {
        $lowest_date = null;
        foreach ($this->events as $event) {
            if (null === $lowest_date || $event->getStart() < $lowest_date) {
                $lowest_date = $event->getStart();
            }
        }

        return $lowest_date;
    }
public function getStart(): ?\DateTimeInterface
    {
        $lowest_date = null;
        foreach ($this->events as $event) {
            if (null === $lowest_date || $event->getStart() < $lowest_date) {
                $lowest_date = $event->getStart();
            }
        }

        return $lowest_date;
    }
public function getStart ( ) : ? \ DateTimeInterface { $ lowest_date = null ; foreach ( $ this -> events as $ event ) { if ( null === $ lowest_date || $ event -> getStart ( ) < $ lowest_date ) { $ lowest_date = $ event -> getStart ( ) ; } } return $ lowest_date ; }
Get the start date of the schedule.

@return ?\DateTimeInterface
Get the start date of the schedule .