code: private function fastlyResize()
      {
          if ($this->getWidth() === null && $this->getHeight() === null) {
              return $this;
          }
  
          $this->adjustSize();
  
          return $this;
      }
docs: Fastly implementation of resize
  
  @see \Magento\Framework\Image\Adapter\AbstractAdapter
  @return \Magento\Catalog\Model\Product\Image