Crashes PHP 7.1.5 when run

<?php
class Foo {
    private $start;
    private $end;
    public function __construct(\DateTimeImmutable $start, \DateTimeImmutable $end)
    {
        $this->start = $start;
        $this->end = $end;
    }
    public function getPeriod()
    {
        return new \DatePeriod($this->start, $this->start->diff($this->end), $this->end);
    }
}

class Bar
{
    private $foos = [];

    public function __construct(array $foos)
    {
        $this->foos = $foos;
    }

    public function getFoos()
    {
        return $this->foos;
    }

    public function doSomething()
    {
        $removePeriods = [];
        $removePeriods[1234] = [];
        foreach ([
                     '2017-06-14 00:00:00' => '2017-06-15 00:00:00',
                     '2017-06-23 00:00:00' => '2017-06-24 00:00:00',
                     '2017-07-04 00:00:00' => '2017-07-05 00:00:00',
                     '2017-07-05 00:00:00' => '2017-07-06 00:00:00',
                     '2017-07-06 00:00:00' => '2017-07-07 00:00:00',
                     '2017-07-25 00:00:00' => '2017-07-26 00:00:00',
                     '2017-07-26 00:00:00' => '2017-07-27 00:00:00',
                     '2017-07-27 00:00:00' => '2017-07-28 00:00:00',
                     '2017-06-12 00:00:00' => '2017-06-13 00:00:00',
                     '2017-06-13 00:00:00' => '2017-06-14 00:00:00',
                     '2017-06-15 00:00:00' => '2017-06-16 00:00:00',
                     '2017-06-16 00:00:00' => '2017-06-17 00:00:00',
                     '2017-06-18 00:00:00' => '2017-06-19 00:00:00',
                     '2017-06-17 00:00:00' => '2017-06-18 00:00:00',
                     '2017-06-24 00:00:00' => '2017-06-25 00:00:00',
                     '2017-06-25 00:00:00' => '2017-06-26 00:00:00',
                     '2017-06-22 00:00:00' => '2017-06-23 00:00:00',
                     '2017-06-21 00:00:00' => '2017-06-22 00:00:00',
                     '2017-06-20 00:00:00' => '2017-06-21 00:00:00',
                     '2017-06-19 00:00:00' => '2017-06-20 00:00:00',
                 ] as $start => $end) {
            $removePeriodStart = new \DateTimeImmutable($start, new \DateTimeZone('Europe/Berlin'));
            $removePeriodEnd = new \DateTimeImmutable($end, new \DateTimeZone('Europe/Berlin'));
            $removePeriods[1234][] = new \DatePeriod(
                $removePeriodStart,
                $removePeriodStart->diff($removePeriodEnd),
                $removePeriodEnd
            );
        }

        foreach ($this->getFoos() as $foo) {
            $periods = [$foo->getPeriod()];

            foreach ($removePeriods[1234] as $removePeriod) {
                $periods = $this->removePeriodFromPeriods($removePeriod, $periods);
            }
        }
    }

    private function removePeriodFromPeriods(\DatePeriod $periodToRemove, array $periods)
    {
        /** @var \DatePeriod[] $periods */
        $periods = array_values($periods);

        $newPeriods = [];
        $newIndex = count($newPeriods);
        foreach ($periods as $index => $period) {
            $newPeriods[$index] = clone $period;

            // Check if the period to remove is outside of the current period (no overlapping)
            if ($periodToRemove->getEndDate() <= $period->getStartDate() ||
                $periodToRemove->getStartDate() >= $period->getEndDate()
            ) {
                continue;
            }

            // Check if the current period is completely overlapped by the period to remove
            $removeStartLowerEqualStart = ($periodToRemove->getStartDate() <= $period->getStartDate());
            $removeEndGreaterEqualEnd = ($periodToRemove->getEndDate() >= $period->getEndDate());
            if ($removeStartLowerEqualStart && $removeEndGreaterEqualEnd) {
                // Unset period
                unset($newPeriods[$index]);
                continue;
            }

            // Check if the beginning of the current period is overlapped by the period to remove
            $removeEndLowerEnd = ($periodToRemove->getEndDate() < $period->getEndDate());
            if ($removeStartLowerEqualStart && $removeEndLowerEnd) {
                // Update period
                $newPeriods[$index] = new \DatePeriod(
                    $periodToRemove->getEndDate(),
                    $periodToRemove->getEndDate()->diff($period->getEndDate()),
                    $period->getEndDate()
                );
                continue;
            }

            // Check if the end of the current period is overlapped by the period to remove
            $removeStartGreaterStart = ($periodToRemove->getStartDate() > $period->getStartDate());
            if ($removeStartGreaterStart && $removeEndGreaterEqualEnd) {
                // Update period
                $newPeriods[$index] = new \DatePeriod(
                    $period->getStartDate(),
                    $period->getStartDate()->diff($periodToRemove->getStartDate()),
                    $periodToRemove->getStartDate()
                );
                continue;
            }

            // Check if the period to remove in contained by the current period
            if ($removeStartGreaterStart && $removeEndLowerEnd) {
                // Update period (to the first part)
                $newPeriods[$index] = new \DatePeriod(
                    $period->getStartDate(),
                    $period->getStartDate()->diff($periodToRemove->getStartDate()),
                    $periodToRemove->getStartDate()
                );
                // Create new period (for the second part)
                $newPeriods[$newIndex++] = new \DatePeriod(
                    $periodToRemove->getEndDate(),
                    $periodToRemove->getEndDate()->diff($period->getEndDate()),
                    $period->getEndDate()
                );
                continue;
            }
        }

        return $newPeriods;
    }
}

$foo = new Foo(
    new \DateTimeImmutable('2017-05-22 09:00:00', new \DateTimeZone('Europe/Berlin')),
    new \DateTimeImmutable('2017-08-24 18:00:00', new \DateTimeZone('Europe/Berlin'))
);
$search = new Bar([$foo]);
$search->doSomething();

echo 'success';

exit;