input: Write a function to convert the given temperature from Celsius to Fahrenheit. The function should take a single argument, which is the temperature in Celsius, and return the temperature in Fahrenheit. If the input is empty, the function should return None.
  assert celsius_to_fahrenheit(0)==32.0
  assert celsius_to_fahrenheit(100)==212.0
  assert celsius_to_fahrenheit(-40)==-40.0
  assert celsius_to_fahrenheit([])==None
  assert celsius_to_fahrenheit(None)==None
output: def celsius_to_fahrenheit(celsius):
      if celsius is None or not isinstance(celsius, (int, float)):
          return None
      return (celsius * 9/5) + 32