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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_if_not_set(self, addresses):
 """Returns the value at an address if it was an input to the txn but never set. It returns None if that address was never set in the merkle database, or if the address is not within the context. Args: addresses (list of str):
 The full 70 character addresses. Returns: (list):
 bytes at that address but not set within the context """


        with self._lock:
            results = []
            for add in addresses:
                results.append(self._get_if_not_set(add))
            return results