input: Write a function called `encrypt_decrypt` that takes a string as input and returns a tuple containing the encrypted and decrypted versions of the string using the AES encryption algorithm. If the input string is empty, the function should return `(None, None)`. Make sure to use a 16-byte key for AES encryption.
  assert encrypt_decrypt("Hello, World!")==(encrypt("Hello, World!"), decrypt(encrypt("Hello, World!")))
  assert encrypt_decrypt("")==(None, None)
output: def encrypt_decrypt(s):
      if not s:
          return (None, None)
      from Crypto.Cipher import AES
      from Crypto.Util.Padding import pad, unpad
      import base64
      key = b'1234567890123456'
      cipher = AES.new(key, AES.MODE_ECB)
      encrypted = base64.b64encode(cipher.encrypt(pad(s.encode(), AES.block_size))).decode()
      decrypted = unpad(cipher.decrypt(base64.b64decode(encrypted)), AES.block_size).decode()
      return (encrypted, decrypted)