make_blank_xml.rb

# coding: utf-8

require 'nokogiri'
require 'active_support/core_ext'


module MakeBlankXML
  class << self
    def execute
      org_doc = Nokogiri::XML(DAMMY_XML)

      blank_doc = Nokogiri::XML::Builder.new(encoding: "utf-8") do |_|
        org_doc.element_children.each do |elem|
          emptify_texts(_, elem)
        end
      end

      puts blank_doc.to_xml
    end

    def emptify_texts(_, elem)
      attributes = nil
      if elem.attributes.present?
        attributes = elem.attributes.inject({}){|h, (k, v)| h[k.intern] = nil; h }
      end

      _.send(elem.name.intern, attributes) do
        # Suppose that if elem.element_children is empty,
        # this block do nothing.
        elem.element_children.each do |child|
          emptify_texts(_, child)
        end
      end
    end
  end

  DAMMY_XML =<<-EOX
<?xml version="1.0" encoding="utf-8"?>
<root xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <person id="002">
        <name>Jet Black</name>
        <age>35</age>
        <properties count="1">
            <ship>Bebop</ship>
        </properties>
    </hoge>
</root>
  EOX
end

result.xml

<?xml version="1.0" encoding="utf-8"?>
<root>
  <person id="">
    <name/>
    <age/>
    <properties count="">
      <ship/>
    </properties>
  </person>
</root>