You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: restart.rb
    path of file: ./repos/kontena/server/app/mutations/stacks
    
    the code of the file until where you have to start completion: module Stacks
  class Restart < Mutations::Command
    include Common

    required do
      model :stack, class: Stack
    end

   
    
    def execute
      self.stack.grid_services.each do |service|
        outcome = GridServices::Restart.run(grid_service: service)
        unless outcome.success?
          handle_service_outcome_errors(service.name, outcome.errors)
        end
      end