def add_card(type = nil, title = nil , subtitle = nil, content = nil)
      # A Card must have a type which the default is Simple.
      @card = Hash.new()
      @card[:type] = type || 'Simple'
      @card[:title] = title unless title.nil?
      @card[:subtitle] = subtitle unless subtitle.nil?
      @card[:content] = content unless content.nil?
      @card
    end
def add_card(type = nil, title = nil , subtitle = nil, content = nil)
      # A Card must have a type which the default is Simple.
      @card = Hash.new()
      @card[:type] = type || 'Simple'
      @card[:title] = title unless title.nil?
      @card[:subtitle] = subtitle unless subtitle.nil?
      @card[:content] = content unless content.nil?
      @card
    end
"type": "string",
    "title": "string",
    "subtitle": "string",
    "content": "string"