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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 fill_nulls(self, col: str):
 """ Fill all null values with NaN values in a column. Null values are ``None`` or en empty string :param col: column name :type col: str :example: ``ds.fill_nulls("mycol")`` """

        n = [None, ""]
        try:
            self.df[col] = self.df[col].replace(n, nan)
        except Exception as e:
            self.err(e)