Put "repair_empty_param_associations" in your before filters in the application_controller.rb

rails 3.2.11 params patch

 def repair_empty_param_associations
    params.keys.each do |key|
      repair_nested_params(params, key, params[key])
    end
  end

  private

  def repair_nested_params(current_params, key, value)
    if key =~ /^(.*)_attributes$/ && value.nil?
      current_params[key] = []
    elsif value.is_a? Hash
      value.keys.each do |nested_key|
        repair_nested_params(value, nested_key, value[nested_key])
      end
    end
  end