input: Write a function to find the maximum value within a nested dictionary.
  
  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": 5})==5
  assert findMaxValue({"key1": { "value1": 10, "value2": 20}, "key2": { "value3": 40}})==40
  assert findMaxValue({"key1": { "value1": 50, "value2": 60}, "key2": { "value3": 40}})==60
  assert findMaxValue({"key1": { "value1": 10, "value2": { "value4": 70}}}, "key2": { "value3": 80})==80
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