input: Write a function to create a basic REST API using Python and Flask to list all the countries in the world. Implement the function to read the list of countries from a JSON file named 'data.json' and return it as a JSON response. If the file does not exist, return an error message.
  assert create_country_api('data.json')=={'countries': ['Afghanistan', 'Albania', 'Algeria', 'Andorra', 'Angola']}
  assert create_country_api('nonexistent.json')=="File not found: nonexistent.json"
  assert create_country_api('')=="File not found: "
  assert create_country_api(None)=="Invalid file name"
output: def create_country_api(file_name):
      if not file_name:
          return "Invalid file name"
      try:
          with open(file_name, 'r') as file:
              data = json.load(file)
              return {'countries': data}
      except FileNotFoundError:
          return f"File not found: {file_name}"