input: Write a function to convert the given temperature from Celsius to Fahrenheit. Given a temperature in Celsius, the function should return the temperature in Fahrenheit. If the input is invalid, the function should return None.
  assert celsius_to_fahrenheit(0) == 32
  assert celsius_to_fahrenheit(100) == 212
  assert celsius_to_fahrenheit(-40) == -40
  assert celsius_to_fahrenheit('invalid') == None
output: def celsius_to_fahrenheit(celsius):
      if isinstance(celsius, (int, float)):
          return (celsius * 9/5) + 32
      else:
          return None