Error using [toc]

[merfed]

I get this: Trying to access array offset on value of type null

on this line:

if (preg_match('/[ ]*{('.$this->regexAttribute.'+)}[ ]*$/', $Block['element']['handler']['argument'], $matches, PREG_OFFSET_CAPTURE)) {

Using this markdown:

[toc]
# One
## Twi
## sfasf
# sdfa

[merfed]

Was able to fix this with these changes:

//
    // Header
    // -------------------------------------------------------------------------

    protected function blockHeader($Line)
    {
        $Block = parent::blockHeader($Line);
        if ($Block !== null && preg_match('/[ #]*{('.$this->regexAttribute.'+)}[ ]*$/', $Block['element']['handler']['argument'], $matches, PREG_OFFSET_CAPTURE)) {
            $attributeString = $matches[1][0];
            $Block['element']['attributes'] = $this->parseAttributeData($attributeString);
            $Block['element']['handler']['argument'] = substr($Block['element']['handler']['argument'], 0, $matches[0][1]);
        }

        // createAnchorID
        if (!isset($Block['element']['attributes']['id']) && isset($Block['element']['handler']['argument'])) {
            $Block['element']['attributes']['id'] = $this->createAnchorID($Block['element']['handler']['argument'], ['transliterate' => false]);
        }

        $link = "#".$Block['element']['attributes']['id'];

        $Block['element']['handler']['argument'] = $Block['element']['handler']['argument']."<a class='heading-link' href='{$link}'> <i class='fas fa-link'></i></a>";

        // ~

        return $Block;
    }

//
    // Setext
    protected function blockSetextHeader($Line, array $Block = null)
    {
        $Block = parent::blockSetextHeader($Line, $Block);

        if ($Block !== null && preg_match('/[ ]*{('.$this->regexAttribute.'+)}[ ]*$/', $Block['element']['handler']['argument'], $matches, PREG_OFFSET_CAPTURE)) {
            $attributeString = $matches[1][0];
            $Block['element']['attributes'] = $this->parseAttributeData($attributeString);
            $Block['element']['handler']['argument'] = substr($Block['element']['handler']['argument'], 0, $matches[0][1]);
        }

        // createAnchorID
        if (!isset($Block['element']['attributes']['id']) && isset($Block['element']['handler']['argument'])) {
            $Block['element']['attributes']['id'] = $this->createAnchorID($Block['element']['handler']['argument'], ['transliterate' => false]);
        }

        if ($Block !== null && $Block['type'] == 'Paragraph') {
            $link = "#".$Block['element']['attributes']['id'];
            $Block['element']['handler']['argument'] = $Block['element']['handler']['argument']."<a class='heading-link' href='{$link}'> <i class='fas fa-link'></i></a>";
        }

        // ~

        return $Block;
    }