input: Write a function to parse a JSON data structure and return the values associated with the keys 'name', 'age', and 'occupation'. If the given JSON data is empty, return None for each key.
  
  def parse_json(data):
   if not data:
    return None, None, None
   data = json.loads(data)
   return data.get('name'), data.get('age'), data.get('occupation')
  
  assert parse_json('{"name": "John", "age": 18, "occupation": "Software Engineer"}')==('John', 18, 'Software Engineer')
  assert parse_json('{"name": "Alice", "age": 22, "occupation": "Teacher"}')==('Alice', 22, 'Teacher')
  assert parse_json('{"name": "Bob", "age": 30, "occupation": ""}')==('Bob', 30, '')
  assert parse_json('{}')==(None, None, None)
  assert parse_json('')==(None, None, None)
output: def parse_json(data):
      if not data:
          return None, None, None
      data = json.loads(data)
      return data.get('name'), data.get('age'), data.get('occupation')