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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 _serialize(self, value, attr, obj):
 """Grab the ID value off the Peewee model so we serialize an ID back. """

        # this might be an optional field
        if value:
            value = value.id

        return super(ForeignKeyField, self)._serialize(value, attr, obj)