代码里面的 isNil 会一直是 false

[winixt]

return val === null && val === undefined; 应该是 return val === null || val === undefined;

export function isNil<T>(val: T | null | undefined): val is null | undefined {
  return val === null && val === undefined;
}

[keuby]

确实存在，非常感谢