input: Write a function to parse a given json-formatted string into a dictionary using Python's json module. The function should return the parsed dictionary. If the input string is not a valid json-formatted string, the function should return None.
  
  import json
  
  def parse_json_to_dict(json_str):
      try:
          return json.loads(json_str)
      except json.JSONDecodeError:
          return None
  
  assert parse_json_to_dict('{"name": "John","age": 30,"address": {"city": "New York","state": "NY"}}')=={"name": "John", "age": 30, "address": {"city": "New York", "state": "NY"}}
  assert parse_json_to_dict('{"name": "Jane","age": "twenty-five","address": {"city": "Los Angeles","state": "CA"}}')=={"name": "Jane", "age": "twenty-five", "address": {"city": "Los Angeles", "state": "CA"}}
  assert parse_json_to_dict('invalid json string')==None
  assert parse_json_to_dict('[]')==[]
  assert parse_json_to_dict('')==None
output: def parse_json_to_dict(json_str):
      try:
          return json.loads(json_str)
      except json.JSONDecodeError:
          return None