input: Write a function to convert the given temperature from Celsius to Fahrenheit. The function should take a Celsius value as input and return the equivalent temperature in Fahrenheit. If the input is empty or invalid, the function should return an appropriate message.
  
  def celsius_to_fahrenheit(celsius):
      if celsius is None or celsius == "":
          return "Invalid input"
      fahrenheit = (celsius * 9/5) + 32
      return fahrenheit
  
  assert celsius_to_fahrenheit(0) == 32
  assert celsius_to_fahrenheit(100) == 212
  assert celsius_to_fahrenheit(-40) == -40
  assert celsius_to_fahrenheit("") == "Invalid input"
  assert celsius_to_fahrenheit(None) == "Invalid input"
output: def celsius_to_fahrenheit(celsius):
      if celsius is None or celsius == "":
          return "Invalid input"
      fahrenheit = (celsius * 9/5) + 32
      return fahrenheit