input: Write a function to convert degrees Fahrenheit to degrees Celsius. The function should take a temperature in Fahrenheit as input and return the equivalent temperature in Celsius. If the input temperature is None, the function should return None.
  assert FahrenheitToCelsius(32) == 0
  assert FahrenheitToCelsius(212) == 100
  assert FahrenheitToCelsius(-40) == -40
  assert FahrenheitToCelsius(None) == None
output: def FahrenheitToCelsius(fahrenheit):
      if fahrenheit is None:
          return None
      return (fahrenheit - 32) * 5 / 9