input: Write a function to find the maximum value within a nested dictionary. The function should recursively search through all nested dictionaries and return the maximum value found.
  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({"key1": {"value1": 10, "value2": 20}, "key2": {"value3": 40}})==40
  assert findMaxValue({"a": 1, "b": 2, "c": {"d": 5, "e": {"f": 3}}})==5
  assert findMaxValue({"g": {"h": {"i": 7}, "j": 6}, "k": 4})==7
  assert findMaxValue({})==None
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