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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 _only_trashed(self, builder):
 """ The only-trashed extension. :param builder: The query builder :type builder: eloquent.orm.builder.Builder """

        model = builder.get_model()

        self.remove(builder, model)

        builder.get_query().where_not_null(model.get_qualified_deleted_at_column())