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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 out_of_bag_mae(self):
 """ Returns the mean absolute error for predictions on the out-of-bag samples. """

        if not self._out_of_bag_mae_clean:
            try:
                self._out_of_bag_mae = self.test(self.out_of_bag_samples)
                self._out_of_bag_mae_clean = True
            except NodeNotReadyToPredict:
                return
        return self._out_of_bag_mae.copy()