[v8] MUI checkbox (is this correct?)

[dcworldwide]

Is the following correct?

function IndeterminateCheckbox({
    indeterminate,
    className = '',
    ...rest
}: { indeterminate?: boolean } & React.HTMLProps<HTMLInputElement>) {

    const ref = React.useRef<HTMLInputElement>(null!)

    React.useEffect(() => {
        if (typeof indeterminate === 'boolean') {
            ref.current.indeterminate = !rest.checked && indeterminate
        }
    }, [ref, indeterminate])

    return <Checkbox
        className={className + ' cursor-pointer'}
        inputRef={ref}
        inputProps={rest}
        checked={rest.checked}
        indeterminate={indeterminate}
    />
}

A few things I"m unsure about:

Passing in inputRef={ref} and inputProps={rest} is correct?
What does the exclamation in React.useRef(null!) do?

Thanks