gistfile1.rb

  def add_css_class(original, add)
    if original.nil?
      return add
    else
      return [original, add].join(' ')
    end
  end

### Use Case

css_class = add_css_class(css_class, 'required') if required

### Or, better!

css_class = [css_class, 'required'].compact.join(' ') if required  # thanks molgrew