input: Write a function to parse a JSON data structure and return the name, age, and occupation from the provided JSON data. If the provided JSON data is empty or missing any required fields, the function should return None for each missing field.
  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}')==('Bob', 30, None)
  assert parse_json('{}')==(None, None, None)
  assert parse_json('{"age": 25, "occupation": "Doctor"}')==(None, 25, 'Doctor')
  assert parse_json('{"name": "Eve", "occupation": "Artist"}')==('Eve', None, 'Artist')
output: import json
  
  def parse_json(json_data):
      data = json.loads(json_data)
      name = data.get('name', None)
      age = data.get('age', None)
      occupation = data.get('occupation', None)
      return (name, age, occupation)