ruby on rails - no implicit conversion of nil into String (sponsorship ) -

i getting above error , says has "+". please note did not code below page, told fix it. if awesome.

mymoh controller

 210. def sponsorships  211. dbdc_client.materialize("cv__recurring_gift__c")  212. #@gifts =cv__recurring_gift__c.find_all_by_cv__contact__c(current_user.convio_id)  213. @gifts = cv__recurring_gift__c.query("cv__contact__c = '" + current_user.convio_id + "' , child_status__c = 'sponsored' , cv__recurring_gift_status__c='active'")  214. @account = contact.find_by_id(current_user.convio_id)  215. #@old_sponsorships = child_sponsorship__c.query("sponsor__c = '" + current_user.convio_id + "' , status__c = 'open'")  216. @sponsorships = @gifts # + @old_sponsorships  217. unless @sponsorships.nil?  218.  #if find sponsorships  219.  @children = []  220.  @sponsorships.each | spons |  221.    @photo = nil  222.      unless spons.child__c.nil?  223.        @child = child__c.find_by_id(spons.child__c)  224.            @phototest = picture__c.query("child__c='" + @child.id + "' , primary__c=true").first  225.            @photo = @phototest.photo__c if @phototest  226.            if @photo.nil?  227.              @attachment = attachment.find_by_parentid(@child.id)  228.              @photo = "<img src='https://c.na12.content.force.com/servlet/servlet.filedownload?file=" + @attachment.id.to_s + "' />" unless @attachment.nil?              end              #set unused variable carry photo url              @child.lastmodifiedbyid = @photo              #add child array of children              @children << @child         end   end end  end 

full trace

app/controllers/mymoh_controller.rb:213:in `+' app/controllers/mymoh_controller.rb:213:in `sponsorships' vendor/bundle/ruby/2.1.0/gems/actionpack-3.2.11/lib/action_controller/metal/implicit_render.rb:4:in `send_action' vendor/bundle/ruby/2.1.0/gems/actionpack-3.2.11/lib/abstract_controller/base.rb:167:in `process_action' vendor/bundle/ruby/2.1.0/gems/actionpack-3.2.11/lib/action_controller/metal/rendering.rb:10:in `process_action' vendor/bundle/ruby/2.1.0/gems/actionpack-3.2.11/lib/abstract_controller/callbacks.rb:18:in `block in process_action' vendor/bundle/ruby/2.1.0/gems/activesupport-3.2.11/lib/active_support/callbacks.rb:425:in `_run__3687996442544047678__process_action__3216127983448203575__callbacks' vendor/bundle/ruby/2.1.0/gems/activesupport-3.2.11/lib/active_support/callbacks.rb:405:in `__run_callback' vendor/bundle/ruby/2.1.0/gems/activesupport-3.2.11/lib/active_support/callbacks.rb:385:in `_run_process_action_callbacks' vendor/bundle/ruby/2.1.0/gems/activesupport-3.2.11/lib/active_support/callbacks.rb:81:in `run_callbacks' vendor/bundle/ruby/2.1.0/gems/actionpack-3.2.11/lib/abstract_controller/callbacks.rb:17:in `process_action' vendor/bundle/ruby/2.1.0/gems/actionpack-3.2.11/lib/action_controller/metal/rescue.rb:29:in `process_action' vendor/bundle/ruby/2.1.0/gems/actionpack-3.2.11/lib/action_controller/metal/instrumentation.rb:30:in `block in process_action' vendor/bundle/ruby/2.1.0/gems/activesupport-3.2.11/lib/active_support/notifications.rb:123:in `block in instrument' vendor/bundle/ruby/2.1.0/gems/activesupport-3.2.11/lib/active_support/notifications/instrumenter.rb:20:in `instrument' vendor/bundle/ruby/2.1.0/gems/activesupport-3.2.11/lib/active_support/notifications.rb:123:in `instrument' vendor/bundle/ruby/2.1.0/gems/actionpack-3.2.11/lib/action_controller/metal/instrumentation.rb:29:in `process_action' vendor/bundle/ruby/2.1.0/gems/actionpack-3.2.11/lib/action_controller/metal/params_wrapper.rb:207:in `process_action' vendor/bundle/ruby/2.1.0/gems/activerecord-3.2.11/lib/active_record/railties/controller_runtime.rb:18:in `process_action' vendor/bundle/ruby/2.1.0/gems/newrelic_rpm-3.11.2.286/lib/new_relic/agent/instrumentation/rails3/action_controller.rb:23:in `block in process_action' vendor/bundle/ruby/2.1.0/gems/newrelic_rpm-3.11.2.286/lib/new_relic/agent/instrumentation/controller_instrumentation.rb:353:in `perform_action_with_newrelic_trace' vendor/bundle/ruby/2.1.0/gems/newrelic_rpm-3.11.2.286/lib/new_relic/agent/instrumentation/rails3/action_controller.rb:22:in `process_action' vendor/bundle/ruby/2.1.0/gems/actionpack-3.2.11/lib/abstract_controller/base.rb:121:in `process' vendor/bundle/ruby/2.1.0/gems/actionpack-3.2.11/lib/abstract_controller/rendering.rb:45:in `process' vendor/bundle/ruby/2.1.0/gems/actionpack-3.2.11/lib/action_controller/metal.rb:203:in `dispatch' vendor/bundle/ruby/2.1.0/gems/actionpack-3.2.11/lib/action_controller/metal/rack_delegation.rb:14:in `dispatch' vendor/bundle/ruby/2.1.0/gems/actionpack-3.2.11/lib/action_controller/metal.rb:246:in `block in action' vendor/bundle/ruby/2.1.0/gems/actionpack-3.2.11/lib/action_dispatch/routing/route_set.rb:73:in `call' vendor/bundle/ruby/2.1.0/gems/actionpack-3.2.11/lib/action_dispatch/routing/route_set.rb:73:in `dispatch' vendor/bundle/ruby/2.1.0/gems/actionpack-3.2.11/lib/action_dispatch/routing/route_set.rb:36:in `call' vendor/bundle/ruby/2.1.0/gems/journey-1.0.4/lib/journey/router.rb:68:in `block in call' vendor/bundle/ruby/2.1.0/gems/journey-1.0.4/lib/journey/router.rb:56:in `each' vendor/bundle/ruby/2.1.0/gems/journey-1.0.4/lib/journey/router.rb:56:in `call' vendor/bundle/ruby/2.1.0/gems/actionpack-3.2.11/lib/action_dispatch/routing/route_set.rb:601:in `call' vendor/bundle/ruby/2.1.0/gems/newrelic_rpm-3.11.2.286/lib/new_relic/agent/instrumentation/middleware_tracing.rb:67:in `call' vendor/bundle/ruby/2.1.0/gems/newrelic_rpm-3.11.2.286/lib/new_relic/rack/agent_hooks.rb:30:in `traced_call' vendor/bundle/ruby/2.1.0/gems/newrelic_rpm-3.11.2.286/lib/new_relic/agent/instrumentation/middleware_tracing.rb:67:in `call' vendor/bundle/ruby/2.1.0/gems/newrelic_rpm-3.11.2.286/lib/new_relic/rack/browser_monitoring.rb:23:in `traced_call' vendor/bundle/ruby/2.1.0/gems/newrelic_rpm-3.11.2.286/lib/new_relic/agent/instrumentation/middleware_tracing.rb:67:in `call' vendor/bundle/ruby/2.1.0/gems/exception_notification-4.0.0/lib/exception_notification/rack.rb:28:in `call' vendor/bundle/ruby/2.1.0/gems/newrelic_rpm-3.11.2.286/lib/new_relic/agent/instrumentation/middleware_tracing.rb:67:in `call' vendor/bundle/ruby/2.1.0/gems/actionpack-3.2.11/lib/action_dispatch/middleware/best_standards_support.rb:17:in `call' vendor/bundle/ruby/2.1.0/gems/newrelic_rpm-3.11.2.286/lib/new_relic/agent/instrumentation/middleware_tracing.rb:67:in `call' vendor/bundle/ruby/2.1.0/gems/rack-1.4.5/lib/rack/etag.rb:23:in `call' vendor/bundle/ruby/2.1.0/gems/newrelic_rpm-3.11.2.286/lib/new_relic/agent/instrumentation/middleware_tracing.rb:67:in `call' vendor/bundle/ruby/2.1.0/gems/rack-1.4.5/lib/rack/conditionalget.rb:25:in `call' vendor/bundle/ruby/2.1.0/gems/newrelic_rpm-3.11.2.286/lib/new_relic/agent/instrumentation/middleware_tracing.rb:67:in `call' vendor/bundle/ruby/2.1.0/gems/actionpack-3.2.11/lib/action_dispatch/middleware/head.rb:14:in `call' vendor/bundle/ruby/2.1.0/gems/newrelic_rpm-3.11.2.286/lib/new_relic/agent/instrumentation/middleware_tracing.rb:67:in `call' vendor/bundle/ruby/2.1.0/gems/actionpack-3.2.11/lib/action_dispatch/middleware/params_parser.rb:21:in `call' vendor/bundle/ruby/2.1.0/gems/newrelic_rpm-3.11.2.286/lib/new_relic/agent/instrumentation/middleware_tracing.rb:67:in `call' vendor/bundle/ruby/2.1.0/gems/actionpack-3.2.11/lib/action_dispatch/middleware/flash.rb:242:in `call' vendor/bundle/ruby/2.1.0/gems/newrelic_rpm-3.11.2.286/lib/new_relic/agent/instrumentation/middleware_tracing.rb:67:in `call' vendor/bundle/ruby/2.1.0/gems/rack-1.4.5/lib/rack/session/abstract/id.rb:210:in `context' vendor/bundle/ruby/2.1.0/gems/rack-1.4.5/lib/rack/session/abstract/id.rb:205:in `call' vendor/bundle/ruby/2.1.0/gems/newrelic_rpm-3.11.2.286/lib/new_relic/agent/instrumentation/middleware_tracing.rb:67:in `call' vendor/bundle/ruby/2.1.0/gems/actionpack-3.2.11/lib/action_dispatch/middleware/cookies.rb:341:in `call' vendor/bundle/ruby/2.1.0/gems/newrelic_rpm-3.11.2.286/lib/new_relic/agent/instrumentation/middleware_tracing.rb:67:in `call' vendor/bundle/ruby/2.1.0/gems/activerecord-3.2.11/lib/active_record/query_cache.rb:64:in `call' vendor/bundle/ruby/2.1.0/gems/newrelic_rpm-3.11.2.286/lib/new_relic/agent/instrumentation/middleware_tracing.rb:67:in `call' vendor/bundle/ruby/2.1.0/gems/activerecord-3.2.11/lib/active_record/connection_adapters/abstract/connection_pool.rb:479:in `call' vendor/bundle/ruby/2.1.0/gems/newrelic_rpm-3.11.2.286/lib/new_relic/agent/instrumentation/middleware_tracing.rb:67:in `call' vendor/bundle/ruby/2.1.0/gems/actionpack-3.2.11/lib/action_dispatch/middleware/callbacks.rb:28:in `block in call' vendor/bundle/ruby/2.1.0/gems/activesupport-3.2.11/lib/active_support/callbacks.rb:405:in `_run__790379348702901205__call__4407048364405463113__callbacks' vendor/bundle/ruby/2.1.0/gems/activesupport-3.2.11/lib/active_support/callbacks.rb:405:in `__run_callback' vendor/bundle/ruby/2.1.0/gems/activesupport-3.2.11/lib/active_support/callbacks.rb:385:in `_run_call_callbacks' vendor/bundle/ruby/2.1.0/gems/activesupport-3.2.11/lib/active_support/callbacks.rb:81:in `run_callbacks' vendor/bundle/ruby/2.1.0/gems/actionpack-3.2.11/lib/action_dispatch/middleware/callbacks.rb:27:in `call' vendor/bundle/ruby/2.1.0/gems/newrelic_rpm-3.11.2.286/lib/new_relic/agent/instrumentation/middleware_tracing.rb:67:in `call' vendor/bundle/ruby/2.1.0/gems/actionpack-3.2.11/lib/action_dispatch/middleware/remote_ip.rb:31:in `call' vendor/bundle/ruby/2.1.0/gems/newrelic_rpm-3.11.2.286/lib/new_relic/agent/instrumentation/middleware_tracing.rb:67:in `call' vendor/bundle/ruby/2.1.0/gems/actionpack-3.2.11/lib/action_dispatch/middleware/debug_exceptions.rb:16:in `call' vendor/bundle/ruby/2.1.0/gems/newrelic_rpm-3.11.2.286/lib/new_relic/agent/instrumentation/middleware_tracing.rb:67:in `call' vendor/bundle/ruby/2.1.0/gems/actionpack-3.2.11/lib/action_dispatch/middleware/show_exceptions.rb:56:in `call' vendor/bundle/ruby/2.1.0/gems/newrelic_rpm-3.11.2.286/lib/new_relic/agent/instrumentation/middleware_tracing.rb:67:in `call' vendor/bundle/ruby/2.1.0/gems/railties-3.2.11/lib/rails/rack/logger.rb:32:in `call_app' vendor/bundle/ruby/2.1.0/gems/railties-3.2.11/lib/rails/rack/logger.rb:16:in `block in call' vendor/bundle/ruby/2.1.0/gems/activesupport-3.2.11/lib/active_support/tagged_logging.rb:22:in `tagged' vendor/bundle/ruby/2.1.0/gems/railties-3.2.11/lib/rails/rack/logger.rb:16:in `call' vendor/bundle/ruby/2.1.0/gems/newrelic_rpm-3.11.2.286/lib/new_relic/agent/instrumentation/middleware_tracing.rb:67:in `call' vendor/bundle/ruby/2.1.0/gems/actionpack-3.2.11/lib/action_dispatch/middleware/request_id.rb:22:in `call' vendor/bundle/ruby/2.1.0/gems/newrelic_rpm-3.11.2.286/lib/new_relic/agent/instrumentation/middleware_tracing.rb:67:in `call' vendor/bundle/ruby/2.1.0/gems/rack-1.4.5/lib/rack/methodoverride.rb:21:in `call' vendor/bundle/ruby/2.1.0/gems/newrelic_rpm-3.11.2.286/lib/new_relic/agent/instrumentation/middleware_tracing.rb:67:in `call' vendor/bundle/ruby/2.1.0/gems/rack-1.4.5/lib/rack/runtime.rb:17:in `call' vendor/bundle/ruby/2.1.0/gems/newrelic_rpm-3.11.2.286/lib/new_relic/agent/instrumentation/middleware_tracing.rb:67:in `call' vendor/bundle/ruby/2.1.0/gems/activesupport-3.2.11/lib/active_support/cache/strategy/local_cache.rb:72:in `call' vendor/bundle/ruby/2.1.0/gems/newrelic_rpm-3.11.2.286/lib/new_relic/agent/instrumentation/middleware_tracing.rb:67:in `call' vendor/bundle/ruby/2.1.0/gems/rack-1.4.5/lib/rack/lock.rb:15:in `call' vendor/bundle/ruby/2.1.0/gems/newrelic_rpm-3.11.2.286/lib/new_relic/agent/instrumentation/middleware_tracing.rb:67:in `call' vendor/bundle/ruby/2.1.0/gems/actionpack-3.2.11/lib/action_dispatch/middleware/static.rb:62:in `call' vendor/bundle/ruby/2.1.0/gems/newrelic_rpm-3.11.2.286/lib/new_relic/agent/instrumentation/middleware_tracing.rb:67:in `call' vendor/bundle/ruby/2.1.0/gems/rack-cache-1.2/lib/rack/cache/context.rb:136:in `forward' vendor/bundle/ruby/2.1.0/gems/rack-cache-1.2/lib/rack/cache/context.rb:245:in `fetch' vendor/bundle/ruby/2.1.0/gems/rack-cache-1.2/lib/rack/cache/context.rb:185:in `lookup' vendor/bundle/ruby/2.1.0/gems/rack-cache-1.2/lib/rack/cache/context.rb:66:in `call!' vendor/bundle/ruby/2.1.0/gems/rack-cache-1.2/lib/rack/cache/context.rb:51:in `call' vendor/bundle/ruby/2.1.0/gems/newrelic_rpm-3.11.2.286/lib/new_relic/agent/instrumentation/middleware_tracing.rb:67:in `call' vendor/bundle/ruby/2.1.0/gems/rack-timeout-0.2.4/lib/rack/timeout.rb:108:in `call' vendor/bundle/ruby/2.1.0/gems/newrelic_rpm-3.11.2.286/lib/new_relic/agent/instrumentation/middleware_tracing.rb:67:in `call' vendor/bundle/ruby/2.1.0/gems/railties-3.2.11/lib/rails/engine.rb:479:in `call' vendor/bundle/ruby/2.1.0/gems/railties-3.2.11/lib/rails/application.rb:223:in `call' vendor/bundle/ruby/2.1.0/gems/railties-3.2.11/lib/rails/railtie/configurable.rb:30:in `method_missing' vendor/bundle/ruby/2.1.0/gems/newrelic_rpm-3.11.2.286/lib/new_relic/agent/instrumentation/middleware_tracing.rb:67:in `call' vendor/bundle/ruby/2.1.0/gems/rack-1.4.5/lib/rack/content_length.rb:14:in `call' vendor/bundle/ruby/2.1.0/gems/railties-3.2.11/lib/rails/rack/log_tailer.rb:17:in `call' vendor/bundle/ruby/2.1.0/gems/thin-1.6.3/lib/thin/connection.rb:86:in `block in pre_process' vendor/bundle/ruby/2.1.0/gems/thin-1.6.3/lib/thin/connection.rb:84:in `catch' vendor/bundle/ruby/2.1.0/gems/thin-1.6.3/lib/thin/connection.rb:84:in `pre_process' vendor/bundle/ruby/2.1.0/gems/thin-1.6.3/lib/thin/connection.rb:53:in `process' vendor/bundle/ruby/2.1.0/gems/thin-1.6.3/lib/thin/connection.rb:39:in `receive_data' vendor/bundle/ruby/2.1.0/gems/eventmachine-1.0.7/lib/eventmachine.rb:187:in `run_machine' vendor/bundle/ruby/2.1.0/gems/eventmachine-1.0.7/lib/eventmachine.rb:187:in `run' vendor/bundle/ruby/2.1.0/gems/thin-1.6.3/lib/thin/backends/base.rb:73:in `start' vendor/bundle/ruby/2.1.0/gems/thin-1.6.3/lib/thin/server.rb:162:in `start' vendor/bundle/ruby/2.1.0/gems/rack-1.4.5/lib/rack/handler/thin.rb:13:in `run' vendor/bundle/ruby/2.1.0/gems/rack-1.4.5/lib/rack/server.rb:268:in `start' vendor/bundle/ruby/2.1.0/gems/railties-3.2.11/lib/rails/commands/server.rb:70:in `start' vendor/bundle/ruby/2.1.0/gems/railties-3.2.11/lib/rails/commands.rb:55:in `block in <top (required)>' vendor/bundle/ruby/2.1.0/gems/railties-3.2.11/lib/rails/commands.rb:50:in `tap' vendor/bundle/ruby/2.1.0/gems/railties-3.2.11/lib/rails/commands.rb:50:in `<top (required)>' script/rails:6:in `require' script/rails:6:in `<main>' 

@pref not declared string assigning " ".

try this:

preferences = string.new if !params[:prefgirl].nil?     preferences = preferences + "girl," end . . . @preferences = preferences