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({"key1": {"value1": 10, "value2": 20}, "key2": {"value3": 40}}) == 40
  assert findMaxValue({"key1": {"value1": 50, "value2": 30}, "key2": {"value3": 45}}) == 50
  assert findMaxValue({"key1": 100, "key2": {"value1": 50}}) == 100
  assert findMaxValue({}) == None
  assert findMaxValue({"key1": 20, "key2": 15, "key3": 25}) == 25
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