input: Write a function to determine if it is possible to create a HTML page that displays a table of contents from the data stored in a database. If it is possible, return 'Yes', else return 'No'. If the input data for the page is missing, return 'No data provided'.
  assert display_toc({})=='Yes'
  assert display_toc({'data': 'table_contents'})=='Yes'
  assert display_toc(None)=='No data provided'
output: def display_toc(data):
      if data is None:
          return 'No data provided'
      return 'Yes'