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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 optional(cls):
 """Return a list of all nullable columns for the resource's table. :rtype: list """

        columns = []
        for column in cls.__table__.columns:  # pylint: disable=no-member
            if column.nullable:
                columns.append(column.name)
        return columns