Rails_admin with rails-api conflict

I have a recently launched project in which I use mongoid for the database and rails_admin to manage it, now I want to have api and I selected rails-api to do this, but for some reason, since I just added rails-api to the gem file, I cannot access the administrator and I always get this error

NoMethodError in Devise :: SessionController # new

undefined `[] 'method for nil: NilClass

and here is the track

warden (1.1.1) lib / warden / session_serializer.rb: 29: in fetch' warden (1.1.1) lib/warden/proxy.rb:196:inuser '(1.1.1) lib / warden / proxy.rb: 293: in _perform_authentication' warden (1.1.1) lib/warden/proxy.rb:90:inauthenticate' warden (1.1.1) lib / warden / proxy.rb : 100: in authenticate?' devise (2.1.0) app/controllers/devise_controller.rb:113:inrequire_no_authentication 'activesupport (3.2.5) lib / active_support / callbacks.rb: 407: in _run__3280997315660744487__process_action__4533000551616940901__callbacks' activesupport (3.2.5) lib/active_support/callbacks.rb:405:in__ run_callback' activesupport (3.2.5) lib / active_support / callbacks.rb: 385: in _run_process_action_callbacks' activesupport (3.2.5) lib/active_support/callbacks.rb:81:inrun_callbacks' actionpack (3.2.5 ) lib / abstract_controller / callbacks.rb: 17: in process_action' actionpack (3.2.5) lib/action_controller/metal/rescue.rb:29:inprocess_action 'actionpack (3.2.5) lib / action_controller / metal / instrumentation.rb: 30: in block in process_action' activesupport (3.2.5) lib/active_support/notifications.rb:123:inblock in instrument' activesupport (3.2.5) lib / active_support / notifications / instrumenter .rb: 20: in instrument' activesupport (3.2.5) lib/active_support/notifications.rb:123:ininstrument 'actionpack (3.2.5) lib / action_controller / metal / instrumentation.rb: 29: inprocess_action' actionpack (3.2.5) lib/action_controller/metal/params_wrapper.rb:206:inprocess_action 'actionpack (3.2.5) lib / abstract_controller / base.rb: 121: in process' actionpack (3.2.5) lib/abstract_controller/rendering.rb:45:inprocess' actionpack (3.2.5) lib / action_controller / metal.rb: 203: in dispatch' actionpack (3.2.5) lib/action_controller/metal/rack_delegation.rb:14:insending' actionpack (3.2.5) lib / action_controller / metal.rb: 246: in block in action' actionpack (3.2.5) lib/action_dispatch/routing/route_set.rb:73:incall 'actionpack (3.2.5) lib / action_dispatch / routing / route_set.rb: 73: in dispatch' actionpack (3.2.5) lib/action_dispatch/routing/route_set.rb:36:incall' actionpack (3.2.5) lib / action_dispatch / routing / mapper.rb: 42: in call' journey (1.0.3) lib/journey/router.rb:68:inblock in call 'travel (1.0.3) lib / travel / router.rb: 56: in each' journey (1.0.3) lib/journey/router.rb:56:incall' actionpack (3.2.5) lib / action_dispatch / routing / route_set.rb: 600: in call' rack-pjax (0.5.9) lib/rack/pjax.rb:12:incall 'mongoid (2.4.10) lib /rack/mongoid/middleware/identity_map.rb: 33: in block in call' mongoid (2.4.10) lib/mongoid.rb:133:inunit_of_work 'mongoid (2.4.10) lib / rack / mongoid / middleware / identity_map.rb: 33: incall' warden (1.1.1) lib/warden/manager.rb:35:inblock in call 'warden (1.1.1) lib / warden / manager.rb: 34: in catch' warden (1.1.1) lib/warden/manager.rb:34:incall' rack (1.4.1) lib / rack / etag.rb: 23: in call' rack (1.4.1) lib/rack/conditionalget.rb:25:incall 'actionpack (3.2.5) lib / action_dispatch / middleware / head.rb: 14: in block in call 'activesupport (3.2.5) lib / active_support / callbacks.rb: 14: in call' remotipart (1.0.2) lib/remotipart/middleware.rb:30:incall' actionpack (3.2.5) lib / action_dispatch / middleware / params_parser.rb: 21 call' actionpack (3.2.5) lib/action_dispatch/middleware/callbacks.rb:28:in: 405: in _run__2911892753477349565__call__1112249857594481255__callbacks' activesupport (3.2.5) lib/active_support/callbacks.rb:405:in__ run_callback 'activesupport (3.2.5) lib / active_support / callbacks.rb: 385: in _run_call_callbacks' activesupport (3.2.5) lib/active_support/callbacks.rb:81:inrun_callbacks' actionpack (3.2.5) lib / action_dispatch / middleware / callbacks.rb: 27: in call' actionpack (3.2.5) lib/action_dispatch/middleware/reloader.rb:65:incall' actionpack (3.2. 5) lib / action_dispatch / middleware / remote_ip.rb: 31: in call' actionpack (3.2.5) lib/action_dispatch/middleware/debug_exceptions.rb:16:incall 'actionpack (3.2.5) lib / action_dispatch / middleware / show_exceptions.rb: 56: incall' railties (3.2.5) lib/rails/rack/logger.rb:26:incall_app 'railties (3.2.5) lib / rails / rack / logger.rb: 16: in call' actionpack (3.2.5) lib/action_dispatch/middleware/request_id.rb:22:incall' rack (1.4.1) lib / rack / runtime.rb: 17: in call' activesupport (3.2.5) lib/active_support/cache/strategy/local_cache.rb:72:incall 'rack (1.4.1) lib / rack / lock.rb: 15: in call' actionpack (3.2.5) lib/action_dispatch/middleware/static.rb:62:incall 'railties (3.2.5) lib / rails / engine.rb: 479: in call' railties (3.2.5) lib/rails/application.rb:220:incall' rack (1.4.1) lib / rack / content_length.rb: 14: in call' railties (3.2.5) lib/rails/rack/log_tailer.rb:17:incall 'rack (1.4.1) lib / rack / handler / webrick.rb: 59: in the `service '

I really have no idea what happens between these gems that trigger this, any advice or direction is welcome;)