input: Write a function to implement an encryption and decryption application using the AES algorithm. The function should take a string as input, encrypt it using a chosen cipher mode, and also provide a decryption function to reverse the encryption. If the input string is empty, return an empty string for both encryption and decryption.
  
  from Crypto.Cipher import AES
  
  key = b'Sixteen byte key'
  
  def encrypt(plaintext):
      if not plaintext:
          return ""
      cipher = AES.new(key, AES.MODE_ECB)
      return cipher.encrypt(plaintext.encode())
  
  def decrypt(ciphertext):
      if not ciphertext:
          return ""
      cipher = AES.new(key, AES.MODE_ECB)
      return cipher.decrypt(ciphertext).decode()
  
  assert encrypt("Hello, World!")!= b"Hello, World!"
  assert decrypt(encrypt("Hello, World!"))== "Hello, World!"
  assert encrypt("")== ""
  assert decrypt("")== ""
output: def encrypt(plaintext):
      if not plaintext:
          return ""
      cipher = AES.new(key, AES.MODE_ECB)
      return cipher.encrypt(plaintext.encode())
  
  def decrypt(ciphertext):
      if not ciphertext:
          return ""
      cipher = AES.new(key, AES.MODE_ECB)
      return cipher.decrypt(ciphertext).decode()