```ruby
class Lesson < ActiveRecord::Base
  attr_accessible :background, :free, :title, :video

  validates :title,      :presence => { :message => "for lesson can't be blank" }
  validates :background, :presence => { :message => "for lesson can't be blank" }

  validate  :free_is_valid
  validate  :url_exists

  belongs_to :course

  def club
    course.club
  end

  def user
    club.user
  end

  def assign_defaults
    self.title      = "Lesson #{(course.lessons.count + 1)} - #{Settings.lessons[:default_title]}"
    self.background = Settings.lessons[:default_background]
    self.free       = Settings.lessons[:default_free]
  end

  private

  def url_exists
    unless video.blank?
      errors.add(:base, "URL is not reachable or malformed - please check your video URL") unless VideoManipulator.validate_url(video)
    end
  end

  def free_is_valid
    unless free.to_s =~ /(true|false)/
      errors.add(:base, "Free must be either true or false")
    end
  end
end
```

Update Text for Lesson free Attribute Error
user
```ruby
class Lesson < ActiveRecord::Base
  attr_accessible :background, :free, :title, :video

  validates :title,      :presence => { :message => "for lesson can't be blank" }
  validates :background, :presence => { :message => "for lesson can't be blank" }

  validate  :free_is_valid
  validate  :url_exists

  belongs_to :course

  def club
    course.club
  end

  def user
    club.user
  end

  def assign_defaults
    self.title      = "Lesson #{(course.lessons.count + 1)} - #{Settings.lessons[:default_title]}"
    self.background = Settings.lessons[:default_background]
    self.free       = Settings.lessons[:default_free]
  end

  private

  def url_exists
    unless video.blank?
      errors.add(:base, "URL is not reachable or malformed - please check your video URL") unless VideoManipulator.validate_url(video)
    end
  end

  def free_is_valid
    unless free.to_s =~ /(true|false)/
      errors.add(:base, "Free for lesson must be either true or false")
    end
  end
end
```
assistant