app/inputs/action_admin/select_list_input.rb
module ActionAdmin
class SelectListInput < SimpleForm::Inputs::CollectionSelectInput
def input(wrapper_options)
input_html_options[:data] ||= {}
input_html_options[:data].merge!({
select_box: '',
list: true,
placeholder: input_html_options[:placeholder]
})
super
end
end
end