get discussion tags in function DiscussionsController_DiscussionMeta_Handler($Sender);

Currently I am writing my own plugin.

I was able to use this function in my plugin to emit some meta data in discussions list.

But I couldn't find how to get each discussion tags.

I try to use following test code, but not found useful information.

echo '<pre>'; var_dump($Sender->Tags); echo '</pre>';
echo '<pre>'; var_dump($Sender->Discussion->Tags); echo '</pre>';

Dump sender will generate a huge list and it's really difficult to find the right one.

echo '<pre>'; var_dump($Sender); echo '</pre>';

Please light me a way! Thank you.