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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 combine_first(self, other):
 """ Combine Series values, choosing the calling Series's values first. Result index will be the union of the two indexes Parameters other : Series Returns ------- y : Series """

        if isinstance(other, SparseSeries):
            other = other.to_dense()

        dense_combined = self.to_dense().combine_first(other)
        return dense_combined.to_sparse(fill_value=self.fill_value)