input: Write a function to convert a JSON-formatted string into a dictionary. Return the resulting dictionary. If the input string is not in valid JSON format, return None.
  assert convert_json_to_dict('{"name": "John", "age": 30, "address": {"city": "New York", "state": "NY"}}')=={'name': 'John', 'age': 30, 'address': {'city': 'New York', 'state': 'NY'}}
  assert convert_json_to_dict('{"name": "Alice", "age": 25}')=={'name': 'Alice', 'age': 25}
  assert convert_json_to_dict('{"key": "value", "array": [1, 2, 3]}')=={'key': 'value', 'array': [1, 2, 3]}
  assert convert_json_to_dict('invalid json')==None
  assert convert_json_to_dict('')==None
output: try:
      import json
      return json.loads(s)
  except json.JSONDecodeError:
      return None