The code infer map keys type as unknown, how to make it work correctly and detect it as string? run it

class HMap<K, V> {
  constructor(items: Record<string, V>)
  constructor(items: [K, V][])
  constructor(items: Record<string, V> | [K, V][]) {
  }
}

const h = new HMap({a: 1, b: 2}) // => HMap<unknown, number>