为什么setIn不可以设置value为null或undefined?

[Volankey]

const setIn = (segments: Segments, source: any, value: any) => {
  for (let i = 0; i < segments.length; i++) {
    const index = segments[i]
    const rules = getDestructor(index as string)
    if (!rules) {
      if (!isValid(source)) return
      if (!isValid(source[index])) {
// 有什么特殊意义吗?
        if (!isValid(source[index]) && !isValid(value)) {
          return
        }
        if (isNum(segments[i + 1])) {
          source[index] = []
        } else {
          source[index] = {}
        }
      }

      if (i === segments.length - 1) {
        source[index] = value
      }

      source = source[index]
    } else {
      setInByDestructor(source, rules, value, { setIn, getIn })
      break
    }
  }
}