Nonce is both required and optional

[MichaelMure]

Maybe I'm missing something, but the nonce is labeled as not required:

nonce Bytes No A unique, random nonce

And later, as required (yet possibly just 0x):

The REQUIRED nonce field MUST include a random nonce. This field ensures that multiple (non-idempotent) invocations are unique. The nonce SHOULD be empty (0x) for Commands that are idempotent (such as deterministic Wasm modules or standards-abiding HTTP PUT requests).

That seems inconsistent.