当我把Ruby on Rails应用程序推到Bluemix时，我已经开始收到这个错误。我的应用程序实际上并不需要数据库，但我在database.yml中有以下内容：

default: &default
  adapter: sqlite3
  pool: 5
  timeout: 5000

development:
  <<: *default
  database: db/development.sqlite3
  
test:
  <<: *default
  database: db/test.sqlite3

production:
  <<: *default
  database: db/production.sqlite3

在我的Gemfile中：

gem 'sqlite3' # Use sqlite3 as the database for Active Record

group :production do
    gem 'rails_serve_static_assets'
end

以下是我得到的错误：

Could not detect rake tasks
ensure you can run `$ bundle exec rake -P` against your app with no environment variables present
and using the production group of your Gemfile.
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/activesupport-4.1.1/lib/active_support/values/time_zone.rb:285: warning: circular argument reference - now
DEPRECATION WARNING: Passing a string to ActiveRecord::Base.establish_connection for a configuration lookup is deprecated, please pass a symbol (:"") instead. (called from <top (required)> at /tmp/staged/app/Rakefile:6)
rake aborted!
ActiveRecord::AdapterNotSpecified: '' database is not configured. Available: ["production"]
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/activerecord-4.1.1/lib/active_record/connection_adapters/connection_specification.rb:257:in `resolve_symbol_connection'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/activerecord-4.1.1/lib/active_record/connection_adapters/connection_specification.rb:240:in `resolve_string_connection'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/activerecord-4.1.1/lib/active_record/connection_adapters/connection_specification.rb:267:in `resolve_hash_connection'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/activerecord-4.1.1/lib/active_record/connection_adapters/connection_specification.rb:228:in `resolve_connection'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/activerecord-4.1.1/lib/active_record/connection_adapters/connection_specification.rb:152:in `resolve'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/activerecord-4.1.1/lib/active_record/connection_adapters/connection_specification.rb:164:in `block in resolve_all'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/activerecord-4.1.1/lib/active_record/connection_adapters/connection_specification.rb:163:in `each'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/activerecord-4.1.1/lib/active_record/connection_adapters/connection_specification.rb:163:in `resolve_all'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/activerecord-4.1.1/lib/active_record/connection_handling.rb:69:in `resolve'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/activerecord-4.1.1/lib/active_record/core.rb:46:in `configurations='
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/activerecord-4.1.1/lib/active_record/core.rb:48:in `block in <module:Core>'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/activesupport-4.1.1/lib/active_support/concern.rb:120:in `class_eval'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/activesupport-4.1.1/lib/active_support/concern.rb:120:in `append_features'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/activerecord-4.1.1/lib/active_record/base.rb:297:in `include'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/activerecord-4.1.1/lib/active_record/base.rb:297:in `<class:Base>'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/activerecord-4.1.1/lib/active_record/base.rb:282:in `<module:ActiveRecord>'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/activerecord-4.1.1/lib/active_record/base.rb:23:in `<top (required)>'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/activerecord-4.1.1/lib/active_record/railtie.rb:39:in `require'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/activerecord-4.1.1/lib/active_record/railtie.rb:39:in `block in <class:Railtie>'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/railties-4.1.1/lib/rails/railtie.rb:237:in `instance_exec'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/railties-4.1.1/lib/rails/railtie.rb:237:in `block in run_tasks_blocks'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/railties-4.1.1/lib/rails/railtie.rb:245:in `each'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/railties-4.1.1/lib/rails/railtie.rb:245:in `each_registered_block'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/railties-4.1.1/lib/rails/railtie.rb:237:in `run_tasks_blocks'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/railties-4.1.1/lib/rails/application.rb:361:in `block in run_tasks_blocks'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/railties-4.1.1/lib/rails/engine/railties.rb:13:in `each'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/railties-4.1.1/lib/rails/engine/railties.rb:13:in `each'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/railties-4.1.1/lib/rails/application.rb:361:in `run_tasks_blocks'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/railties-4.1.1/lib/rails/engine.rb:449:in `load_tasks'
/tmp/staged/app/Rakefile:6:in `<top (required)>'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/rake-11.1.2/lib/rake/rake_module.rb:28:in `load'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/rake-11.1.2/lib/rake/rake_module.rb:28:in `load_rakefile'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/rake-11.1.2/lib/rake/application.rb:689:in `raw_load_rakefile'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/rake-11.1.2/lib/rake/application.rb:94:in `block in load_rakefile'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/rake-11.1.2/lib/rake/application.rb:176:in `standard_exception_handling'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/rake-11.1.2/lib/rake/application.rb:93:in `load_rakefile'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/rake-11.1.2/lib/rake/application.rb:77:in `block in run'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/rake-11.1.2/lib/rake/application.rb:176:in `standard_exception_handling'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/rake-11.1.2/lib/rake/application.rb:75:in `run'
/tmp/staged/app/vendor/bundle/ruby/2.2.0/gems/rake-11.1.2/bin/rake:33:in `<top (required)>'
vendor/bundle/bin/rake:16:in `load'
vendor/bundle/bin/rake:16:in `<main>'
###### WARNING:
You have not declared a Ruby version in your Gemfile.
To set your Ruby version add this line to your Gemfile:
ruby '2.2.3'