The `RAILS5=1 rspec spec/controllers/admin/application_settings_controller_spec.rb`
command throws the error:

Failures:

  1) Admin::ApplicationSettingsController PUT #update falls back to defaults when settings are omitted
      Failure/Error: import_sources = params[:application_setting][:import_sources]

      NoMethodError:
        undefined method `[]' for nil:NilClass
      # ./app/controllers/admin/application_settings_controller.rb:62:in `application_setting_params'

This commit fixes it.