multivalue feature columns: dataset.batch report different shape

[advancera]

when i use multivalue feature, such as [['a', 'b', 'c'], ['a', 'b']].
the program will report bug like: cannot batch elements of different shape. element 0 has shape [3], but element 1 has shape [2].
i know the different shape of multivalue feature result in this bug.
i think the function Dataset.padded_batch maybe solve the problem, i write like dataset = dataset.padded_batch(5, padded_shapes=[None]), it reported bug TypeError: If shallow structure is a sequence, input must also be a sequence. Input has type: list
so, how can i process the multivalue exactly?
i am eager to solve this problem, can anyboby help me? thanks a lot!