input: Write a function to find the maximum value within a nested dictionary. If the given dictionary is empty then return None.
  def findMaxValue(dict):
      max_val = None
      for key, value in dict.items():
          if isinstance(value, dict):
              max_val = max(findMaxValue(value), max_val)
          else:
              max_val = max(value, max_val)
      return max_val
  
  assert findMaxValue({})==None
  assert findMaxValue({"key1": 10})==10
  assert findMaxValue({"key1": 10, "key2": 20})==20
  assert findMaxValue({"key1": {"value1": 10, "value2": 20}, "key2": {"value3": 40}})==40
output: def findMaxValue(dict):
      max_val = None
      for key, value in dict.items():
          if isinstance(value, dict):
              max_val = max(findMaxValue(value), max_val)
          else:
              max_val = max(value, max_val)
      return max_val