readable.push('')
不推荐使用 readable.push('')。
将零字节字符串、Buffer 或 Uint8Array 推送到非对象模式的流有一个有趣的副作用。
因为是对 readable.push() 的调用，所以调用会结束读取过程。
然而，因为参数是空字符串，没有数据被添加到可读缓冲区，所以用户没有任何东西可以消费。
Use of readable.push('') is not recommended.
Pushing a zero-byte string, Buffer, or Uint8Array to a stream that is not in
object mode has an interesting side effect. Because it is a call to
readable.push(), the call will end the reading process.
However, because the argument is an empty string, no data is added to the
readable buffer so there is nothing for a user to consume.