獲取一個未定義的方法'+'爲零：NilClass error

我想要做的是記錄用戶獲得的睡眠量，然後能夠顯示基於每月範圍的每月中值睡眠量，以及每年的範圍。 current_user是設計人員的助手，並且睡眠belongs_to用戶。用戶has_many睡覺。獲取一個未定義的方法'+'爲零：NilClass error

控制器：

def index 
    @date = params[:date] ? Date.parse(params[:date]) : Date.today 

    @sleeps = current_user.sleeps 
    respond_to do |format| 
    format.html { render action: 'index' } 
    format.js 
    end 

    total_average_sleep_time = Array.new 
    @sleeps.each do |average| 
    average = average.hours 
    total_average_sleep_time.push(average) 
    end 
    @total_average_sleep_time = median(total_average_sleep_time) 

    month_range = current_user.sleeps.where(:sleep_date => @[email protected]_of_month) 
    monthly_average_sleep_time = Array.new 
    month_range.each do |average| 
    average = average.hours 
    monthly_average_sleep_time.push(average) 
    end 
    @monthly_average_sleep_time = median(monthly_average_sleep_time) 
end 

private 

def median(array) 
    sorted = array.sort 
    len = sorted.length 
    return (sorted[(len - 1)/2] + sorted[len/2])/2.0 
end

完整的錯誤消息：

Started GET "/sleeps" for 127.0.0.1 at 2013-06-21 18:34:50 -0700 
Processing by SleepsController#index as HTML 
    User Load (0.4ms) SELECT "users".* FROM "users" WHERE "users"."id" = 2 LIMIT 1 
    Sleep Load (0.3ms) SELECT "sleeps".* FROM "sleeps" WHERE "sleeps"."user_id" = 2 
    Rendered sleeps/index.html.erb within layouts/application (17.1ms) 
Completed 500 Internal Server Error in 115ms 

NoMethodError (undefined method `+' for nil:NilClass): 
app/controllers/sleeps_controller.rb:69:in `median' 
app/controllers/sleeps_controller.rb:16:in `index' 


Rendered /Users/james/.rvm/gems/ruby-2.0.0-p195/gems/actionpack-3.2.13/lib/action_dispatch/middleware/templates/rescues/_trace.erb (1.0ms) 
Rendered /Users/james/.rvm/gems/ruby-2.0.0-p195/gems/actionpack-3.2.13/lib/action_dispatch/middleware/templates/rescues/_request_and_response.erb (0.8ms) 
Rendered /Users/james/.rvm/gems/ruby-2.0.0-p195/gems/actionpack-3.2.13/lib/action_dispatch/middleware/templates/rescues/diagnostics.erb within rescues/layout (6.6ms)

完全跟蹤：

app/controllers/sleeps_controller.rb:69:in `median' 
app/controllers/sleeps_controller.rb:16:in `index' 
actionpack (3.2.13) lib/action_controller/metal/implicit_render.rb:4:in `send_action' 
actionpack (3.2.13) lib/abstract_controller/base.rb:167:in `process_action' 
actionpack (3.2.13) lib/action_controller/metal/rendering.rb:10:in `process_action' 
actionpack (3.2.13) lib/abstract_controller/callbacks.rb:18:in `block in process_action' 
activesupport (3.2.13) lib/active_support/callbacks.rb:414:in `_run__271727191433844250__process_action__1430197560934326917__callbacks' 
activesupport (3.2.13) lib/active_support/callbacks.rb:405:in `__run_callback' 
activesupport (3.2.13) lib/active_support/callbacks.rb:385:in `_run_process_action_callbacks' 
activesupport (3.2.13) lib/active_support/callbacks.rb:81:in `run_callbacks' 
actionpack (3.2.13) lib/abstract_controller/callbacks.rb:17:in `process_action' 
actionpack (3.2.13) lib/action_controller/metal/rescue.rb:29:in `process_action' 
actionpack (3.2.13) lib/action_controller/metal/instrumentation.rb:30:in `block in process_action' 
activesupport (3.2.13) lib/active_support/notifications.rb:123:in `block in instrument' 
activesupport (3.2.13) lib/active_support/notifications/instrumenter.rb:20:in `instrument' 
activesupport (3.2.13) lib/active_support/notifications.rb:123:in `instrument' 
actionpack (3.2.13) lib/action_controller/metal/instrumentation.rb:29:in `process_action' 
actionpack (3.2.13) lib/action_controller/metal/params_wrapper.rb:207:in `process_action' 
activerecord (3.2.13) lib/active_record/railties/controller_runtime.rb:18:in `process_action' 
actionpack (3.2.13) lib/abstract_controller/base.rb:121:in `process' 
actionpack (3.2.13) lib/abstract_controller/rendering.rb:45:in `process' 
actionpack (3.2.13) lib/action_controller/metal.rb:203:in `dispatch' 
actionpack (3.2.13) lib/action_controller/metal/rack_delegation.rb:14:in `dispatch' 
actionpack (3.2.13) lib/action_controller/metal.rb:246:in `block in action' 
actionpack (3.2.13) lib/action_dispatch/routing/route_set.rb:73:in `call' 
actionpack (3.2.13) lib/action_dispatch/routing/route_set.rb:73:in `dispatch' 
actionpack (3.2.13) lib/action_dispatch/routing/route_set.rb:36:in `call' 
journey (1.0.4) lib/journey/router.rb:68:in `block in call' 
journey (1.0.4) lib/journey/router.rb:56:in `each' 
journey (1.0.4) lib/journey/router.rb:56:in `call' 
actionpack (3.2.13) lib/action_dispatch/routing/route_set.rb:612:in `call' 
omniauth (1.1.4) lib/omniauth/strategy.rb:184:in `call!' 
omniauth (1.1.4) lib/omniauth/strategy.rb:164:in `call' 
warden (1.2.1) lib/warden/manager.rb:35:in `block in call' 
warden (1.2.1) lib/warden/manager.rb:34:in `catch' 
warden (1.2.1) lib/warden/manager.rb:34:in `call' 
actionpack (3.2.13) lib/action_dispatch/middleware/best_standards_support.rb:17:in `call' 
rack (1.4.5) lib/rack/etag.rb:23:in `call' 
rack (1.4.5) lib/rack/conditionalget.rb:25:in `call' 
actionpack (3.2.13) lib/action_dispatch/middleware/head.rb:14:in `call' 
actionpack (3.2.13) lib/action_dispatch/middleware/params_parser.rb:21:in `call' 
actionpack (3.2.13) lib/action_dispatch/middleware/flash.rb:242:in `call' 
rack (1.4.5) lib/rack/session/abstract/id.rb:210:in `context' 
rack (1.4.5) lib/rack/session/abstract/id.rb:205:in `call' 
actionpack (3.2.13) lib/action_dispatch/middleware/cookies.rb:341:in `call' 
activerecord (3.2.13) lib/active_record/query_cache.rb:64:in `call' 
activerecord (3.2.13) lib/active_record/connection_adapters/abstract/connection_pool.rb:479:in `call' 
actionpack (3.2.13) lib/action_dispatch/middleware/callbacks.rb:28:in `block in call' 
activesupport (3.2.13) lib/active_support/callbacks.rb:405:in `_run__3592650198556540672__call__1302268635398135570__callbacks' 
activesupport (3.2.13) lib/active_support/callbacks.rb:405:in `__run_callback' 
activesupport (3.2.13) lib/active_support/callbacks.rb:385:in `_run_call_callbacks' 
activesupport (3.2.13) lib/active_support/callbacks.rb:81:in `run_callbacks' 
actionpack (3.2.13) lib/action_dispatch/middleware/callbacks.rb:27:in `call' 
actionpack (3.2.13) lib/action_dispatch/middleware/reloader.rb:65:in `call' 
actionpack (3.2.13) lib/action_dispatch/middleware/remote_ip.rb:31:in `call' 
actionpack (3.2.13) lib/action_dispatch/middleware/debug_exceptions.rb:16:in `call' 
actionpack (3.2.13) lib/action_dispatch/middleware/show_exceptions.rb:56:in `call' 
railties (3.2.13) lib/rails/rack/logger.rb:32:in `call_app' 
railties (3.2.13) lib/rails/rack/logger.rb:16:in `block in call' 
activesupport (3.2.13) lib/active_support/tagged_logging.rb:22:in `tagged' 
railties (3.2.13) lib/rails/rack/logger.rb:16:in `call' 
actionpack (3.2.13) lib/action_dispatch/middleware/request_id.rb:22:in `call' 
rack (1.4.5) lib/rack/methodoverride.rb:21:in `call' 
rack (1.4.5) lib/rack/runtime.rb:17:in `call' 
activesupport (3.2.13) lib/active_support/cache/strategy/local_cache.rb:72:in `call' 
rack (1.4.5) lib/rack/lock.rb:15:in `call' 
actionpack (3.2.13) lib/action_dispatch/middleware/static.rb:63:in `call' 
railties (3.2.13) lib/rails/engine.rb:479:in `call' 
railties (3.2.13) lib/rails/application.rb:223:in `call' 
rack (1.4.5) lib/rack/content_length.rb:14:in `call' 
railties (3.2.13) lib/rails/rack/log_tailer.rb:17:in `call' 
rack (1.4.5) lib/rack/handler/webrick.rb:59:in `service' 
/Users/james/.rvm/rubies/ruby-2.0.0-p195/lib/ruby/2.0.0/webrick/httpserver.rb:138:in `service' 
/Users/james/.rvm/rubies/ruby-2.0.0-p195/lib/ruby/2.0.0/webrick/httpserver.rb:94:in `run' 
/Users/james/.rvm/rubies/ruby-2.0.0-p195/lib/ruby/2.0.0/webrick/server.rb:295:in `block in start_thread'

可爲什麼發生這種情況的人向我解釋？它在控制檯中完美工作。有沒有更清晰的方法來調試這樣的問題？我知道這是由於中位數方法的增加，但爲什麼？

來源

2013-06-22 JamesDullaghan

這可以用下面的表達式生成：'nil + 10' - 那它是什麼意思？那麼，這意味着'nil'（'NilClass'類型）出現在二進制'+'運算符的*左邊*上。所以找出並修復它。 – user2246674

你可以把整個錯誤信息？ – Syl

它怎麼可能在一個地方是零，而不是在另一個地方？控制檯工作，而控制器不工作。 – JamesDullaghan