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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 force_extrapolation(self):
 """Force the underlying model to extrapolate. An example where this is useful: You create a source spectrum with non-default extrapolation behavior and you wish to force the underlying empirical model to extrapolate based on nearest point. .. note:: This is only applicable to `~synphot.models.Empirical1D` model and should still work even if the source spectrum has been redshifted. Returns ------- is_forced : bool `True` if the model is successfully forced to be extrapolated, else `False`. """

        # We use _model here in case the spectrum is redshifted.
        if isinstance(self._model, Empirical1D):
            self._model.fill_value = np.nan
            is_forced = True
        else:
            is_forced = False

        return is_forced