Call to a member function get() on null

Dear coleagues,
few weeks ago we've been facing strange error displaying sermon detail, series etc. Displayed error is "Call to a member function get() on null", but I'm not able to find, where the problem is. I've uninstalled and re-installed Sermon Speaker and I've restored table contents. I've also reinstalled used template, but with no success. Could you give me some hints? How to log such errors, how to find which class, method and in which file error have occured. And best, if you have had similar problems, how you solved it?

Web page , error page is Sermon detail page or Sermon serie .

Thank you
Best regards
Petr

Looks like I messed up something in the recent release. I'll try to figure out what happend.

Can you try what happens when you disable the BibleLink XT plugin (if you have that installed)?

Dear Thomas,
first of all - THANK YOU for such good tool, as Sermon Speaker is. We are using it since our web page redesign, many people asked us, what is it and I've been recomending it every time .
But to your notes - we don't have this plugin installed. And what is strange even more - on our "dev" web everything is working fine .

Thank you again
Best regards
Petr

Heureka! I've got it - I've found the place, where to put echo $this->renderBacktrace(); (template/.../error.php) and it revealed, that problem was caused somehow by calling
plgContentPhocaOpenGraph->onContentAfterDisplay() from /libraries/joomla/event/event.php.

I've disabled this plugin and everything works as should

Thank you again for your effort and time.

Have a nice time
Best regards
Petr

Ah thank you. I can reproduce the same issue on sermonspeaker.net (disabling BibleLink XT does the trick here, hence my question), but also not on my development enviroment.
So I can at least now limit it to the onContentAfterDisplay call and content plugins.