input: Write a function to create an encryption and decryption application in Python. The application should take a string as input and use the AES cipher algorithm in ECB mode to encrypt and decrypt the string. If the input string is empty, the function should return an empty string.
  from Crypto.Cipher import AES
  
  key = b'Sixteen byte key'
  
  def encrypt_decrypt_aes_ecb(text, mode):
      if text == "":
          return ""
      cipher = AES.new(key, AES.MODE_ECB)
      if mode == "encrypt":
          return cipher.encrypt(text)
      elif mode == "decrypt":
          return cipher.decrypt(text)
  
  assert encrypt_decrypt_aes_ecb("Hello World", "encrypt") != "Hello World"
  assert encrypt_decrypt_aes_ecb(encrypt_decrypt_aes_ecb("Hello World", "encrypt"), "decrypt") == "Hello World"
  assert encrypt_decrypt_aes_ecb("", "encrypt") == ""
  assert encrypt_decrypt_aes_ecb("", "decrypt") == ""
output: from Crypto.Cipher import AES
  
  key = b'Sixteen byte key'
  
  def encrypt_decrypt_aes_ecb(text, mode):
      if text == "":
          return ""
      cipher = AES.new(key, AES.MODE_ECB)
      if mode == "encrypt":
          return cipher.encrypt(text)
      elif mode == "decrypt":
          return cipher.decrypt(text)