```ruby
class CarnivalEnumInput < SimpleForm::Inputs::CollectionSelectInput

  def input(wrapper_options = nil)
    options[:collection] ||= get_collection
    super
  end

  def input_html_classes
    super.push('form-control')
  end

  def get_collection
    object.class.const_get(constant_name)
  end

  def constant_name
    "#{attribute_name.upcase}_ENUM"
  end
end
```

Fix CarnivalEnumInput default nil parameter value in input method
user
```ruby
class CarnivalEnumInput < SimpleForm::Inputs::CollectionSelectInput

  def input(wrapper_options = nil)
    options[:collection] ||= get_collection
    super()
  end

  def input_html_classes
    super.push('form-control')
  end

  def get_collection
    object.class.const_get(constant_name)
  end

  def constant_name
    "#{attribute_name.upcase}_ENUM"
  end
end
```
assistant