```ruby
require 'erb'

module Arbre
  module HTML

    class TextNode < Element

      builder_method :text_node

      # Builds a text node from a string
      def self.from_string(string)
        node = new
        node.build(string)
        node
      end

      def add_child(*args)
        raise "TextNodes do not have children"
      end

      def build(string)
        @content = string
      end

      def tag_name
        nil
      end

      def to_s
        ERB::Util.html_escape(@content.to_s)
      end
    end

  end
end
```

Fix searching elements by class name from a tree including a text node by implementing the missing class_list method
user
```ruby
require 'erb'

module Arbre
  module HTML

    class TextNode < Element

      builder_method :text_node

      # Builds a text node from a string
      def self.from_string(string)
        node = new
        node.build(string)
        node
      end

      def add_child(*args)
        raise "TextNodes do not have children"
      end

      def build(string)
        @content = string
      end

      def class_list
        []
      end

      def tag_name
        nil
      end

      def to_s
        ERB::Util.html_escape(@content.to_s)
      end
    end

  end
end
```
assistant