stream: readable.push(undefined) behaviour?

[ronag]

Noticed this while working on #29762.

What is the expected behaviour of:

const readable = new Readable({ objectMode: false });
readable.push(); // readable.push(undefined);

It seems to get through chunkInvalid https://github.com/nodejs/node/blob/master/lib/_stream_readable.js#L340

But can later fail with a null ref at Stream._uint8ArrayToBuffer https://github.com/nodejs/node/blob/master/lib/_stream_readable.js#L279

Unless I'm missing something, shouldn't it really be a ERR_INVALID_ARG_TYPE?

[ronag]

@addaleax @mcollina