Fix issue with attempting to write to a nil session store

It is possible and valid to have no session store configured (e.g. when
using warden from a purely API-accessed app). SessionSerializer throws
an exception if a rack session does not exist due to trying to access it.
This changes the session to be injected to SessionSerializer and defaults
it to a hash if no session exists (basically a NullSession). Fixes
https://github.com/plataformatec/devise/issues/2065
Add test for nil session store specifically
Merge pull request #75 from latortuga/allow-nil-session-store

Fix issue with attempting to write to a nil session store
Do not throw exception on logout if session is nil. Fixes #78
Merge pull request #79 from emilsoman/nil-session-logout

Do not throw exception on logout if session is nil. Fixes #78 , #37
Release v1.2.2
Support lazily loaded sessions
Release v1.2.3
Removed Ruby warnings.
Don't change Gemfile.lock.
Fix typo
Merge pull request #83 from kurioscreative/patch-1

Fix typo
Merge pull request #80 from tbuehlmann/warnings

Ruby warnings
fixed typo and improved wording
Update common.rb

fix method doc typo
fix typo
Merge pull request #92 from zishe/typo

fix typos
Merge pull request #87 from mlpinit/cleanup/typo_and_wording

Cleanup - typo and wording
Merge pull request #89 from dguzzo/patch-1

Update common.rb
raise an exception if the scope is not a symbol or string