v3 Cloud: CreateIssue assignee not working

[uncaught]

This SDK suggests that the issue assignee could be sent along when creating an issue. However, this doesn't appear to be valid.

out/version3/parameters/createIssue.d.ts

export interface CreateIssue extends Omit<IssueUpdateDetails, 'fields'> {
    // ...
    fields: {
        [key: string]: any;
        // ...
        assignee?: {
            [key: string]: any;
            id?: string | number;
        };
    };
}

I've tried numerous ways to both set no assignee and set a specific assignee, but all come back as 400:

// Unassigned:
{fields: {assignee: null}}
{fields: {assignee: {id: null}}}
{fields: {assignee: {id: -1}}}
{fields: {assignee: {accountId: null}}}
{fields: {assignee: {accountId: -1}}}

// Assigned:
{fields: {assignee: {id: "xxx-my-account-id"}}}
{fields: {assignee: {accountId: "xxx-my-account-id"}}}
{fields: {assignee: "xxx-my-account-id"}}

According to a discussion here it is not possible to set the assignee to "Unassigned" directly, so that's that, nothing you can do about it and the types don't suggest this anyway.

However, setting an explicit account id also doesn't work.