input: Write a function to store and retrieve user data in a JSON file. The function should write user data to a file named "user_data.json" and read user data from the same file. If the file does not exist, it should return an empty dictionary.
  
  
  import json
  
  user_data = {"Name": "John", "Age": 25, "City": "New York"}
  
  def store_user_data(data):
      with open('user_data.json', 'w') as f:
          json.dump(data, f)
  
  def get_user_data():
      try:
          with open('user_data.json') as f:
              return json.load(f)
      except FileNotFoundError:
          return {}
  
  # Test cases
  assert store_user_data(user_data) is None
  assert get_user_data() == {"Name": "John", "Age": 25, "City": "New York"}
  assert store_user_data({}) is None
  assert get_user_data() == {}
  
output: 
  def store_user_data(data):
      with open('user_data.json', 'w') as f:
          json.dump(data, f)
  
  def get_user_data():
      try:
          with open('user_data.json') as f:
              return json.load(f)
      except FileNotFoundError:
          return {}
  