Set the byte data and fill up the bytes to fit the size.

def data(self, value):
        """Set the byte data and fill up the bytes to fit the size."""
        if not value:
            value = b''
        if len(value) > self.SIZE:
            raise ValueError("The maximum tag size is {0}".format(self.SIZE))
        self._data = value
        while len(self._data) < self.SIZE:
            self._data += b'\x00'