input: Write a function to construct an XML document using Python which contains a list of items provided as input. If the list is empty, the function should return an XML document with no items. The function should return the XML document as a string.
  assert construct_xml_document(['Item1', 'Item2', 'Item3']) == '<data><item>Item1</item><item>Item2</item><item>Item3</item></data>'
  assert construct_xml_document([]) == '<data/>'
output: def construct_xml_document(items):
      if not items:
          return '<data/>'
      xml_items = ''.join(f'<item>{item}</item>' for item in items)
      return f'<data>{xml_items}</data>'