When e.g. specifying an invalid 'reference' value for an IMAP server to
a root folder that does not exist, we would previously have crashed with
a nonsensical and non-intuitive error message (trying to address an
element of a NoneType).
This will also raise an Exception (which should be ok, given that this
is really a misconfiguration on the user side), but it will explain to
the user WHY it exited.
Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>
Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>