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": 10, "key2": 20})==20
  assert findMaxValue({"key1": {"subkey1": 30}, "key2": 20})==30
  assert findMaxValue({"key1": {"subkey1": 30, "subkey2": 50}, "key2": {"subkey3": 40}})==50
  assert findMaxValue({"key1": {"subkey1": 30, "subkey2": {"subsubkey": 70}}})==70
  assert findMaxValue({"key1": {"subkey1": {"subsubkey": 70}, "subkey2": 50}})==70
  assert findMaxValue({"key1": {"subkey1": {"subsubkey": 70}, "subkey2": {"subsubkey2": 90}}})==90
  assert findMaxValue({"key1": {"subkey1": {"subsubkey": 70}, "subkey2": {"subsubkey2": {"subsubsubkey": 100}}}})==100
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