Issue #3240181 by alexpott: \Drupal\datetime\DateTimeComputed::getValue()...

    $item = $this->getParent();

    $value = $item->{($this->definition->getSetting('date source'))};

    // A date cannot be created from a NULL value.

    if ($value === NULL) {

      return NULL;

    }

    $datetime_type = $item->getFieldDefinition()->getSetting('datetime_type');

    $storage_format = $datetime_type === DateTimeItem::DATETIME_TYPE_DATE ? DateTimeItemInterface::DATE_STORAGE_FORMAT : DateTimeItemInterface::DATETIME_STORAGE_FORMAT;

    try {