input: Write a function to parse a JSON data structure. The function should take a JSON string as input, parse it, and return the name, age, and occupation fields from the parsed data. If the input data is not valid JSON, the function should catch the exception and return None.
  
  import json
  
  def parse_json(data):
   try:
    parsed_data = json.loads(data)
    return parsed_data['name'], parsed_data['age'], parsed_data['occupation']
   except (json.JSONDecodeError, KeyError):
    return None
  
  data = '{"name": "John", "age": 18, "occupation": "Software Engineer"}'
  assert parse_json(data) == ("John", 18, "Software Engineer")
  
  data = '{"name": "Jane", "age": 25}'
  assert parse_json(data) == None
  
  data = 'not a JSON string'
  assert parse_json(data) == None
output: 
  def parse_json(data):
   try:
    parsed_data = json.loads(data)
    return parsed_data['name'], parsed_data['age'], parsed_data['occupation']
   except (json.JSONDecodeError, KeyError):
    return None
  