[Dovecot] v2.2 getting NULL pointer reference with shared namespace in mailbox_tree?

[Walter Steiner]

> I can't seem to be able to reproduce this. What's in the user's subscriptions file?

Did some doveadm mailbox (un)subscribe -u ... 

If the file subscriptions in the mailbox of this user is

a)
empty
=> crash

b)
user.otherexistinguser.existingfolder
=> crash

c)
user.other...
INBOX
=> okay

d)
INBOX
=> okay

d)
test
=> okay

It seems that with an active shared namespace one needs to have
at least one folder in the private namespace in this file.

With no shared namespace the list may be empty.

(the client did not automatically subscribe to mailboxes (before the lsub))