input: Write a function to create an application in Python for encryption and decryption of strings using the AES cipher algorithm. The application should take a string as input, use the provided key, and return the encrypted or decrypted string based on the operation performed. If the input string is empty, the function should return an empty string.
  assert encrypt("Hello, World!")==b'\xb1)\xcf+7\xea\xd9{\xfc\x8a\x96\x1f\xe0\xbe\x12'
  assert decrypt(b'\xb1)\xcf+7\xea\xd9{\xfc\x8a\x96\x1f\xe0\xbe\x12')=="Hello, World!"
  assert encrypt("")==""
  assert decrypt("")==""
output: from Crypto.Cipher import AES
  from Crypto.Util.Padding import pad, unpad
  import base64
  
  def encrypt(text):
      if not text:
          return ""
      key = b'Sixteen byte key'
      cipher = AES.new(key, AES.MODE_ECB)
      encrypted_text = cipher.encrypt(pad(text.encode(), AES.block_size))
      return base64.b64encode(encrypted_text)
  
  def decrypt(encrypted_text):
      if not encrypted_text:
          return ""
      key = b'Sixteen byte key'
      cipher = AES.new(key, AES.MODE_ECB)
      decrypted_text = unpad(cipher.decrypt(base64.b64decode(encrypted_text)), AES.block_size)
      return decrypted_text.decode()