message: Update encrypt-and-decrypt-strings.py
diff: @@ -24,6 +24,8 @@ class Encrypter(object):
  :type word1: str
  :rtype: str
  """
  + if any(c not in self.__lookup for c in word1):
  + return ""
  return "".join(self.__lookup[c] for c in word1)
  def decrypt(self, word2):
  