Uncaught exception Zend_Session_Exception if invalid session id was received

[Stafox]

Uncaught exception 'Zend_Session_Exception' with message 'The session has already been started. The session id must be set first.' in library/Zend/Session.php:667

This happens if invalid session id was received, for example: Cookie: PHPSESSID=(null) and session has already been started in bootstrap.

Because if self::_checkId(self::getId()) returns false, it tried to generate a valid, temporary replacement for session id using
self::setId(md5(self::getId()));
this caught the exception.

It can be reproduced using curl:
curl -X POST -H "Cookie: PHPSESSID=(null)" http://zf1project.local/

Be sure that session has been started in bootstrap.