User tests: Successful: Unsuccessful:
Add a default value when the JArrayHelper::fromObject does not return a valid data.
The object might not have the __toString function so in some case there was a fatal error.
If you want to have the error, just but this code:
$_SESSION['test'] = new stdClass();
http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=29517
Please create a tracker on joomlacode with precise instructions to reproduce the issue with default core or providing an extension to test and cross reference here.