hole dataframe first line is missing

[mhallipelto]

[ahartikainen]

        dict_list = self.survey.data
        if not dict_list:
            msg = "No data in Hole object. Header: {}".format(self.__str__())
            logger.warning(msg)
            return pd.DataFrame()
        self._dataframe = pd.DataFrame(dict_list)  # pylint: disable=attribute-defined-outside-init
        self._dataframe.columns = ["data_{}".format(col) for col in self._dataframe.columns]
        if not self._dataframe.empty:
            self._dataframe.loc[0, self._dataframe.columns] = np.nan
        for key in self.header.keys:
            self._dataframe.loc[:, "Date"] = self.header.date
            for key_, item in getattr(self.header, key).items():
                self._dataframe.loc[:, "header_{}_{}".format(key, key_)] = item
        for key in self.fileheader.keys:
            for key_, item in getattr(self.fileheader, key).items():
                self._dataframe.loc[:, "fileheader_{}_{}".format(key, key_)] = item

[ahartikainen]

self._dataframe.loc[0, self._dataframe.columns] = np.nan

why do we do this?