def user_json(user)
  {
   'display_name' => user.display_name,
   'reputation' => user.reputation unless user.reputation,
   'age' => user.age, unless user.age
   'location' => user.location, unless user.location
   'website_url' => user.website_url, unless user.website_url
   'profile_image' => user.profile_image, unless user.profile_image
end