XF 2.3 Only functions with whitelisted prefixes are allowed

[Gavo]

After updating to 2.3.7 an addon I made no longer works, is there any info on this error documented I cant find anything.

Oops! We ran into some problems.
Line 2: The function getimdbid may not be called in a template. Only functions with whitelisted prefixes are allowed. - Template name: public:imdb

In Template.

<xf:if is="{$thread.getimdbid("id")}">

Entity

namespace Imdb\Info\Entity;

class Thread extends XFCP_Thread
    {
    public function getImdbid($imdbget)
        {
        $message = $this->FirstPost->message;
        preg_match('/imdb.com\/title\/tt([0-9]*)/',$message,$matches);

.......

Thanks