input: Write a function to determine if a given string is a palindrome, which means it reads the same backward as forward. If the string is a palindrome, return True; otherwise, return False. If the string is empty or None, return True.
  def is_palindrome(s):
      '''This function returns True if the string s is a palindrome and False if it isn't.''' 
      return s == s[::-1]  # Checks if s is the same as its reverse.
  assert is_palindrome("racecar")==True
  assert is_palindrome("hello")==False
  assert is_palindrome("madam")==True
  assert is_palindrome("a")==True
  assert is_palindrome("")==True
  assert is_palindrome(None)==True
output: def is_palindrome(s):
      if s is None or s == "":
          return True
      return s == s[::-1]