input: Write a function to construct an XML document using Python which contains the given list of items. If the list is empty, the function should create an empty XML document with the root element named 'data'.
  assert construct_xml(['Item1', 'Item2', 'Item3']) is None
  assert construct_xml([]) is None
output: 
  def construct_xml(items):
      if not items:
          return "<data></data>"
      xml = "<data>"
      for item in items:
          xml += f"<item>{item}</item>"
      xml += "</data>"
      return xml
  