The error:

2016-02-09T14:45:14 [app] [W] Action failed
 | AbstractController::DoubleRenderError: Render and/or redirect were called multiple times in this action. Please note that you may only call render OR redirect, and at most once per action. Also note that neither redirect nor render terminate execution of the action, so if you want to exit an action after redirecting, you need to do something like "redirect_to(...) and return".
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/action_controller/metal/rendering.rb:15:in `render'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/action_controller/metal/instrumentation.rb:41:in `block (2 levels) in render'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/core_ext/benchmark.rb:12:in `block in ms'
 | /home/vagrant/.rvm/rubies/ruby-2.2.0/lib/ruby/2.2.0/benchmark.rb:303:in `realtime'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/core_ext/benchmark.rb:12:in `ms'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/action_controller/metal/instrumentation.rb:41:in `block in render'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/action_controller/metal/instrumentation.rb:84:in `cleanup_view_runtime'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activerecord-4.1.5/lib/active_record/railties/controller_runtime.rb:25:in `cleanup_view_runtime'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/action_controller/metal/instrumentation.rb:40:in `render'
 | /home/vagrant/foreman/app/controllers/api/base_controller.rb:86:in `not_found'
 | /home/vagrant/foreman/app/controllers/api/base_controller.rb:230:in `block in not_found_if_nested_id_exists'
 | /home/vagrant/foreman/app/controllers/api/base_controller.rb:228:in `each'
 | /home/vagrant/foreman/app/controllers/api/base_controller.rb:228:in `not_found_if_nested_id_exists'
 | /home/vagrant/foreman/app/controllers/api/base_controller.rb:216:in `find_optional_nested_object'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:424:in `block in make_lambda'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:143:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:143:in `block in halting_and_conditional'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:149:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:149:in `block in halting_and_conditional'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:166:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:166:in `block in halting'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:299:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:299:in `block (2 levels) in halting'
 | /home/vagrant/foreman/app/controllers/api/v2/base_controller.rb:152:in `disable_json_root'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:424:in `block in make_lambda'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:298:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:298:in `block in halting'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:166:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:166:in `block in halting'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:149:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:149:in `block in halting_and_conditional'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:229:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:229:in `block in halting'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:299:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:299:in `block (2 levels) in halting'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/rails-observers-0.1.2/lib/rails/observers/action_controller/caching/sweeping.rb:73:in `around'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:447:in `public_send'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:447:in `block in make_lambda'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:298:in `block in halting'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:299:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:299:in `block (2 levels) in halting'
 | /home/vagrant/foreman/app/controllers/concerns/application_shared.rb:13:in `set_timezone'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:424:in `block in make_lambda'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:298:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:298:in `block in halting'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:149:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:149:in `block in halting_and_conditional'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:149:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:149:in `block in halting_and_conditional'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:166:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:166:in `block in halting'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:166:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:166:in `block in halting'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:149:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:149:in `block in halting_and_conditional'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:166:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:166:in `block in halting'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:149:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:149:in `block in halting_and_conditional'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:229:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:229:in `block in halting'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:299:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:299:in `block (2 levels) in halting'
 | /home/vagrant/foreman/app/models/concerns/foreman/thread_session.rb:32:in `clear_thread'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:424:in `block in make_lambda'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:298:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:298:in `block in halting'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:229:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:229:in `block in halting'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:166:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:166:in `block in halting'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:166:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:166:in `block in halting'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:166:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:166:in `block in halting'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:299:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:299:in `block (2 levels) in halting'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/rails-observers-0.1.2/lib/rails/observers/action_controller/caching/sweeping.rb:73:in `around'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:447:in `public_send'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:447:in `block in make_lambda'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:298:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:298:in `block in halting'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:149:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:149:in `block in halting_and_conditional'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:86:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:86:in `run_callbacks'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/abstract_controller/callbacks.rb:19:in `process_action'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/action_controller/metal/rescue.rb:29:in `process_action'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/action_controller/metal/instrumentation.rb:31:in `block in process_action'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/notifications.rb:159:in `block in instrument'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/notifications/instrumenter.rb:20:in `instrument'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/notifications.rb:159:in `instrument'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/action_controller/metal/instrumentation.rb:30:in `process_action'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/action_controller/metal/params_wrapper.rb:250:in `process_action'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activerecord-4.1.5/lib/active_record/railties/controller_runtime.rb:18:in `process_action'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/abstract_controller/base.rb:136:in `process'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionview-4.1.5/lib/action_view/rendering.rb:30:in `process'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/action_controller/metal.rb:196:in `dispatch'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/action_controller/metal/rack_delegation.rb:13:in `dispatch'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/action_controller/metal.rb:232:in `block in action'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/action_dispatch/routing/route_set.rb:82:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/action_dispatch/routing/route_set.rb:82:in `dispatch'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/action_dispatch/routing/route_set.rb:50:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/action_dispatch/routing/mapper.rb:45:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/action_dispatch/journey/router.rb:71:in `block in call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/action_dispatch/journey/router.rb:59:in `each'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/action_dispatch/journey/router.rb:59:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/action_dispatch/routing/route_set.rb:678:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/action_dispatch/middleware/static.rb:64:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/action_dispatch/middleware/static.rb:64:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/apipie-rails-0.3.5/lib/apipie/static_dispatcher.rb:65:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/bullet-5.0.0/lib/bullet/rack.rb:12:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/apipie-rails-0.3.5/lib/apipie/extractor/recorder.rb:132:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/apipie-rails-0.3.5/lib/apipie/middleware/checksum_in_headers.rb:27:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/rack-openid-1.4.2/lib/rack/openid.rb:98:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/rack-1.5.5/lib/rack/etag.rb:23:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/rack-1.5.5/lib/rack/conditionalget.rb:35:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/rack-1.5.5/lib/rack/head.rb:11:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/action_dispatch/middleware/params_parser.rb:27:in `call'
 | /home/vagrant/foreman/lib/middleware/catch_json_parse_errors.rb:9:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/action_dispatch/middleware/flash.rb:254:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/rack-1.5.5/lib/rack/session/abstract/id.rb:225:in `context'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/rack-1.5.5/lib/rack/session/abstract/id.rb:220:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/action_dispatch/middleware/cookies.rb:560:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activerecord-4.1.5/lib/active_record/query_cache.rb:36:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activerecord-4.1.5/lib/active_record/connection_adapters/abstract/connection_pool.rb:621:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activerecord-4.1.5/lib/active_record/migration.rb:380:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/action_dispatch/middleware/callbacks.rb:29:in `block in call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/callbacks.rb:82:in `run_callbacks'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/action_dispatch/middleware/callbacks.rb:27:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/action_dispatch/middleware/reloader.rb:73:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/action_dispatch/middleware/remote_ip.rb:76:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/action_dispatch/middleware/debug_exceptions.rb:17:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/action_dispatch/middleware/show_exceptions.rb:30:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/railties-4.1.5/lib/rails/rack/logger.rb:38:in `call_app'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/railties-4.1.5/lib/rails/rack/logger.rb:22:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/quiet_assets-1.1.0/lib/quiet_assets.rb:27:in `call_with_quiet_assets'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/action_dispatch/middleware/request_id.rb:21:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/rack-1.5.5/lib/rack/methodoverride.rb:21:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/rack-1.5.5/lib/rack/runtime.rb:17:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/activesupport-4.1.5/lib/active_support/cache/strategy/local_cache_middleware.rb:26:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/rack-1.5.5/lib/rack/lock.rb:17:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/actionpack-4.1.5/lib/action_dispatch/middleware/static.rb:64:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/rack-1.5.5/lib/rack/sendfile.rb:112:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/railties-4.1.5/lib/rails/engine.rb:514:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/railties-4.1.5/lib/rails/application.rb:144:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/railties-4.1.5/lib/rails/railtie.rb:194:in `public_send'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/railties-4.1.5/lib/rails/railtie.rb:194:in `method_missing'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/rack-1.5.5/lib/rack/builder.rb:138:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/rack-1.5.5/lib/rack/urlmap.rb:65:in `block in call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/rack-1.5.5/lib/rack/urlmap.rb:50:in `each'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/rack-1.5.5/lib/rack/urlmap.rb:50:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/rack-1.5.5/lib/rack/lock.rb:17:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/rack-1.5.5/lib/rack/content_length.rb:14:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/rack-1.5.5/lib/rack/handler/webrick.rb:60:in `service'
 | /home/vagrant/.rvm/rubies/ruby-2.2.0/lib/ruby/2.2.0/webrick/httpserver.rb:138:in `service'
 | /home/vagrant/.rvm/rubies/ruby-2.2.0/lib/ruby/2.2.0/webrick/httpserver.rb:94:in `run'
 | /home/vagrant/.rvm/rubies/ruby-2.2.0/lib/ruby/2.2.0/webrick/server.rb:294:in `block in start_thread'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/logging-2.0.0/lib/logging/diagnostic_context.rb:448:in `call'
 | /home/vagrant/.rvm/gems/ruby-2.2.0/gems/logging-2.0.0/lib/logging/diagnostic_context.rb:448:in `block in create_with_logging_context'
2016-02-09T14:45:14 [app] [I] Completed 500 Internal Server Error in 25ms
2016-02-09T14:45:14 [app] [F]
 | AbstractController::DoubleRenderError (Render and/or redirect were called multiple times in this action. Please note that you may only call render OR redirect, and at most once per action. Also note that neither redirect nor render terminate execution of the action, so if you want to exit an action after redirecting, you need to do something like "redirect_to(...) and return".):
 |   app/controllers/api/v2/base_controller.rb:143:in `render_error'
 |   app/controllers/api/base_controller.rb:22:in `block in <class:BaseController>'
 |   lib/middleware/catch_json_parse_errors.rb:9:in `call'
 |
 |

Here is the JSON I used:

{
    "environment_id": null,
    "hostgroup_id": null,
    "organization_id": 1,
    "location_id": 2,
    "name": "new hostname" 
}

The problem appears to be here:

https://github.com/theforeman/foreman/blob/develop/app/controllers/api/base_controller.rb#L227-L233

If more than one of these special attributes are included and also null then the result is more than one render:

(byebug) allowed_nested_id
["hostgroup_id", "location_id", "organization_id", "environment_id"]

I would expect null attributes to be accepted and that they would remove the association. If this is not a valid assumption then the API should provide an appropriate error.
h3. Steps to Reproduce

1. PUT to a host with JSON similar to the above
2. Note 500 ISE