Not able to execute rails test related commands

I am new to rails and trying to execute the test cases of an existing application but I am getting the below error.

[vagrant@localhost scams]$ RAILS_ENV=test rake db:migrate
rake aborted!
NoMethodError: undefined method `symbolize_keys' for nil:NilClass
/home/vagrant/myapp/scams/config/initializers/load_app_config.rb:2:in `<top (required)>'
/home/vagrant/.rvm/gems/ruby-2.1.0/gems/activesupport-4.2.7.1/lib/active_support/dependencies.rb:268:in `load'
/home/vagrant/.rvm/gems/ruby-2.1.0/gems/activesupport-4.2.7.1/lib/active_support/dependencies.rb:268:in `block in load'
/home/vagrant/.rvm/gems/ruby-2.1.0/gems/activesupport-4.2.7.1/lib/active_support/dependencies.rb:240:in `load_dependency'
/home/vagrant/.rvm/gems/ruby-2.1.0/gems/activesupport-4.2.7.1/lib/active_support/dependencies.rb:268:in `load'
/home/vagrant/.rvm/gems/ruby-2.1.0/gems/railties-4.2.7.1/lib/rails/engine.rb:652:in `block in load_config_initializer'
/home/vagrant/.rvm/gems/ruby-2.1.0/gems/activesupport-4.2.7.1/lib/active_support/notifications.rb:166:in `instrument'
/home/vagrant/.rvm/gems/ruby-2.1.0/gems/railties-4.2.7.1/lib/rails/engine.rb:651:in `load_config_initializer'
/home/vagrant/.rvm/gems/ruby-2.1.0/gems/railties-4.2.7.1/lib/rails/engine.rb:616:in `block (2 levels) in <class:Engine>'
/home/vagrant/.rvm/gems/ruby-2.1.0/gems/railties-4.2.7.1/lib/rails/engine.rb:615:in `each'

Someone please help to get rid of this error. I guess I am missing some steps.