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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 NextToken(self):
 """Retrieves the next token. Returns: The next token (instance of Token) or None. """

    # If we don't have enough data - feed ourselves: We assume
    # that we must have at least one sector in our buffer.
    if len(self.buffer) < 512:
      if self.Feed() == 0 and not self.buffer:
        return None

    return Lexer.NextToken(self)