What version of Go are you using (go version)?

$ go version
1.15beta1

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

$ go env

What did you do?

What did you expect to see?

Because there is no New function supplied for bufioWriter2kPool and bufioWriter4kPool, every time pool Get return nil.
`
func newBufioWriterSize(w io.Writer, size int) *bufio.Writer {

    pool := bufioWriterPool(size)  // should  delete or supply New func
    if pool != nil {
            if v := pool.Get(); v != nil {
                    bw := v.(*bufio.Writer)
                    bw.Reset(w)
                    return bw
            }
    }
    return bufio.NewWriterSize(w, size)

}
`

What did you see instead?