Let update() methods clear a field by sending null #1135

Update methods use None as the default for every keyword argument and drop unset arguments from the payload (_resource_client.py#L154-L187). That leaves no way to send null for a top-level field the API lets you clear, for example a run's generalAccess (run.py#L80-L105) or a storage's name to make it unnamed.

The JS client sends the update object as given, so run.update({ generalAccess: null }) clears the field (run.ts#L682-L692).

Expected behavior

Update methods tell an unset argument apart from an explicit None, for example with a sentinel default, and send null for an explicit None on fields the API allows to be cleared. Changing the defaults changes the public signatures, so this belongs in 4.0.

✍️ Drafted by Claude Code