Args:
            X: DataFrame with NaN's
        Returns:
            Dictionary with one key - 'X' corresponding to given DataFrame but without nan's

def transform(self, X):
        """
        Args:
            X: DataFrame with NaN's
        Returns:
            Dictionary with one key - 'X' corresponding to given DataFrame but without nan's

        """
        if self.fill_missing:
            X = self.filler.complete(X)
        return {'X': X}