Not clear how to construct "None"

I'm trying to invoke the equivalent of this python API: https://www.tensorflow.org/api_docs/python/tf/transpose

where perm=None by default.

Digging into the API I found Ops.linalg.transpose() but the perm parameter is mandatory, and I can't figure out how to construct the equivalent of None. So I have two questions:

1. Should the perm parameter be optional?
2. How does one construct None?

首先阅读 Ops.linalg.transpose()，并将其必需参数 perm 与链接的 Python tf.transpose API 进行比较。确定缺少 perm 时预期的 Java 表示形式，以及该参数是否应为可选参数；当 API 行为及其覆盖范围确定后，即表示完成。