Where is Magento session serialized?

Question

I am getting this fatal error:

PHP Fatal error:  
Uncaught exception 'Exception' with message 
'Serialization of 'Mage_Core_Model_Config_Element' is not allowed' 
in [no active file]:0 Stack trace: #0 {main}   
thrown in [no active file] on line 0

I understand it is trying to serialize Mage_Core_Model_Config_Element and failing, yet I have never used getNode(), it's always getStoreConfig() for me.

I am happy to debug this, if I could just find WHERE it is being generated. Where is the Magento session being serialized?

Note: trying to echo the serialization in footer (like one thread suggested) does not work in this case. The session is not being set (cause of this error) and so there is no error when it gets to the footer...

Answer 1

I have found the error that caused this. However was interested in finding out where is the place to debug this, but as there is no proper answer to this, no reason to wait longer.

Anyways, the problem is adding a model object to session, which obviously then is a no-no. At one point or another it must contain that class of an element.