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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 get_thumbnail_source(self, obj):
 """ Obtains the source image field for the thumbnail. :param obj: An object with a thumbnail_field defined. :return: Image field for thumbnail or None if not found. """

        if hasattr(self, 'thumbnail_field') and self.thumbnail_field:
            return resolve(obj, self.thumbnail_field)

        # try get_list_image, from ListableMixin
        if hasattr(obj, 'get_list_image'):
            return resolve(obj, "get_list_image")

        logger.warning('ThumbnailAdminMixin.thumbnail_field unspecified')
        return None