Transformer/SlugifyTransformer.php
public function transform($value, array $options = [])
    {
        $resolver = new OptionsResolver();
        $this->configureOptions($resolver);
        $options = $resolver->resolve($options);

        $transliterator = \Transliterator::create($options['transliterator']);
        $string = $transliterator->transliterate($value);

        return trim(
            preg_replace(
                $options['replace'],
                $options['separator'],
                strtolower(trim(strip_tags($string)))
            ),
            $options['separator']
        );
    }
public function transform($value, array $options = [])
    {
        $resolver = new OptionsResolver();
        $this->configureOptions($resolver);
        $options = $resolver->resolve($options);

        $transliterator = \Transliterator::create($options['transliterator']);
        $string = $transliterator->transliterate($value);

        return trim(
            preg_replace(
                $options['replace'],
                $options['separator'],
                strtolower(trim(strip_tags($string)))
            ),
            $options['separator']
        );
    }
Must return the transformed $value

@param mixed $value
@param array $options

@throws \Symfony\Component\OptionsResolver\Exception\ExceptionInterface

@return mixed $value