input: Write a function to create an application in Python for encryption and decryption of strings using the AES algorithm. The application should take a string as input, encrypt it using a ciphertext algorithm of choice, and return the encrypted string. Additionally, it should have a function to decrypt the encrypted string and return the original plaintext. If the input string is empty, return an empty string for both encryption and decryption functions.
  
  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)
  
  def decrypt(ciphertext):
      if not ciphertext:
          return ''
      cipher = AES.new(key, AES.MODE_ECB)
      return cipher.decrypt(ciphertext)
  
  assert encrypt('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)
  
  def decrypt(ciphertext):
      if not ciphertext:
          return ''
      cipher = AES.new(key, AES.MODE_ECB)
      return cipher.decrypt(ciphertext)