Call to a member function getAttributeText() on null

Question

I have created an dropdown attribute programatically. Now i am trying to get an attribute value inside the class using object manager but unfortunately i am facing an error

function getServiceScheduleSlotss() is were i need the attribute value which is then called inside the function getAllOptions().

This is the Error i found in the error.log

"PHP Fatal error: Uncaught Error: Call to a member function getAttributeText() on null in /var/www/html/magento2sample/app/code/Today/Slot/Model/Config/Source/Options.php:20"

Is there anyway to get attribute value here without using Object manager , If not how to solve this issue?

Also i have used this same method to get attribute value to a phtml using block and worked fine

<?php 
namespace Today\Slot\Model\Config\Source;

use Magento\Eav\Model\ResourceModel\Entity\Attribute\OptionFactory;
use Magento\Framework\DB\Ddl\Table;

class Options extends \Magento\Eav\Model\Entity\Attribute\Source\AbstractSource
{ 
    /**
     * Get all options
     *
     * @return array
     */


    function getServiceScheduleSlotss() {

    $objectManager = \Magento\Framework\App\ObjectManager::getInstance(); 
    $product = $objectManager->get('Magento\Framework\Registry')->registry('current_product');
    $slot_break = $product->getAttributeText('choose_slot_break');
    $slot_interval = $product->getAttributeText('choose_slot_intervel');
    $time_period_from = $product->getAttributeText('time_period_from');
    $time_period_to = $product->getAttributeText('time_period_to');
    $date_from = $product->getchooseDateFrom();
    $date_to = $product->getchooseDateTo();
    $slot_break = substr($slot_break,0,2);
    $slot_interval = substr($slot_interval,0,2);
    $date_from = substr($date_from,0,10);
    $date_to = substr($date_to,0,10); 

        $start = new \DateTime($time_period_from);
        $end = new \DateTime($time_period_to);
        $interval = new \DateInterval("PT" . $slot_interval. "M");
        $slot_breakInterval = new \DateInterval("PT" . $slot_break. "M");

        for ($intStart = $start; 
             $intStart < $end; 
             $intStart->add($interval)->add($slot_breakInterval)) {

               $endPeriod = clone $intStart;
               $endPeriod->add($interval);
               if ($endPeriod > $end) {
                 $endPeriod=$end;
               }
               $periods[] = $intStart->format('H:iA') . 
                            ' - ' . 
                            $endPeriod->format('H:iA');
        }

        return $periods;
    }


    public function getAllOptions()
    {
        $periods = $this->getServiceScheduleSlotss();
        $this->_options = [ 
            ['label'=>'', 'value'=>''],
            ['label'=>'10-11', 'value'=>'1'],
            ['label'=>'12-13', 'value'=>'2'],
            ['label'=>'15-16', 'value'=>'3']
        ];
        return $this->_options;
    }

    /**
     * Get a text for option value
     *
     * @param string|integer $value
     * @return string|bool
     */
    public function getOptionText($value)
    {
        foreach ($this->getAllOptions() as $option) {
            if ($option['value'] == $value) {
                return $option['label'];
            }
        }
        return false;
    }
}