TYPO3 Core

In this function:

    public function render($conf = [])
    {
        $imageResource = NULL;
        $lastImgResourceInfo = $this->cObj->getImgResource($conf['file'] ?? '', $conf['file.'] ?? []);
        if ($this->hasTypoScriptFrontendController()) {
            $this->getTypoScriptFrontendController()->lastImgResourceInfo = $lastImgResourceInfo;
        }
        if (!is_array($lastImgResourceInfo)) {
            return '';
        }
        $imageResource = $lastImgResourceInfo[3];
        return isset($conf['stdWrap.']) ? $this->cObj->stdWrap($imageResource, $conf['stdWrap.']) : $imageResource;
    }

    public function render($conf = [])
    {
        $imageResource = NULL;
        $lastImgResourceInfo = $this->cObj->getImgResource($conf['file'] ?? '', $conf['file.'] ?? []);
        if ($this->hasTypoScriptFrontendController()) {
            $this->getTypoScriptFrontendController()->lastImgResourceInfo = $lastImgResourceInfo;
        }
        if (!is_array($lastImgResourceInfo)) {
            return '';
        }
        if (isset($lastImgResourceInfo[3])){
            $imageResource = $lastImgResourceInfo[3];
        }
        return isset($conf['stdWrap.']) ? $this->cObj->stdWrap($imageResource, $conf['stdWrap.']) : $imageResource;
    }

under some circumstances $lastImgResourceInfo³ won't be set.
This results in a php warning.

Maybe change likt this?

   public function render($conf = [])
    {
        $imageResource = NULL;
        $lastImgResourceInfo = $this->cObj->getImgResource($conf['file'] ?? '', $conf['file.'] ?? []);
        if ($this->hasTypoScriptFrontendController()) {
            $this->getTypoScriptFrontendController()->lastImgResourceInfo = $lastImgResourceInfo;
        }
        if (!is_array($lastImgResourceInfo)) {
            return '';
        }
        if (isset($lastImgResourceInfo[3])){
            $imageResource = $lastImgResourceInfo[3];
        }
        return isset($conf['stdWrap.']) ? $this->cObj->stdWrap($imageResource, $conf['stdWrap.']) : $imageResource;
    }