Unable to activate the plugin, a message is displayed: Call to a member function getInfo() on null.
It's strange, after a couple of days I tried to install the plugin again - it was installed and turned on! However, the "Save"button does not work in the plugin settings...
Manually added settings to conf/config.php:
$Configuration['Plugins']['DiscussionPolls']['EnableShowResults'] = true;
$Configuration['Plugins']['DiscussionPolls']['DisablePollTitle'] = true;
I got the same error. In my case it was caused by a mismatch between the plugin's name and the plugin folder's name. Apparently, those need to be identical.
So, check that your plugin folder's name matches your plugin's name (i.e. its key value in addon.json). :)