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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 add_key_value(self, key, value):
 """Add custom field to Group object. .. note:: The key must be the exact name required by the batch schema. Example:: document = tcex.batch.group('Document', 'My Document') document.add_key_value('fileName', 'something.pdf') Args: key (str):
 The field key to add to the JSON batch data. value (str):
 The field value to add to the JSON batch data. """

        key = self._metadata_map.get(key, key)
        if key in ['dateAdded', 'eventDate', 'firstSeen', 'publishDate']:
            self._group_data[key] = self._utils.format_datetime(
                value, date_format='%Y-%m-%dT%H:%M:%SZ'
            )
        elif key == 'file_content':
            # file content arg is not part of Group JSON
            pass
        else:
            self._group_data[key] = value