Type '... | null' is not assignable to type '...'. (when using useRef array)

When using useRef as DOMElemenet array type this error occured.

const checkPointRef = useRef<HTMLDivElement[]>([]);

<div ref={(elem) => (checkPointRef.current[0] = elem)} />

As error says, 'elem' variable, which refers to div element, can be null. So the correct type for the useRef([]) would be
<(HTMLDivElement | null)>[]

const checkPointRef = useRef<(null | HTMLDivElement)[]>([]);