fix: support setting null account sid

[aarya-brex]

Fixes

Account SID is a nullable field, we should allow setting the accountSid to null for users managing multiple rest clients

Checklist

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[childish-sambino]

Works for me. Thanks!

[aarya-brex]

Will you be able to cut us a new version?

[childish-sambino]

Next release is scheduled for tomorrow (generally, every second Wednesday).