Rails: Group by day showing empty days

group_by_day.rb

notifications = Notifications.where('notifications.created_at BETWEEN ? AND ?', start_date, end_date)
notifications_by_date = notifications.group_by { |notification| notification.created_at.to_date }
@notifications_by_day = (start_date.to_date..end_date.to_date).map do |date|
  {
    day: date,
    notifications: notifications_by_date[date] || [],
  }
end
@notifications_by_day.reverse!