encoding/json: can't omit empty value with type time.Time while encoding struct to json payload?

[thinkhy]

Please answer these questions before submitting your issue. Thanks!

1. What version of Go are you using (go version)?
   go version go1.6 darwin/amd64
2. What operating system and processor architecture are you using (go env)?
   GOARCH="amd64"
   GOBIN=""
   GOEXE=""
   GOHOSTARCH="amd64"
   GOHOSTOS="darwin"
   GOOS="darwin"
   GOPATH="/Users/thinkhy/go"
   GORACE=""
   GOROOT="/usr/local/Cellar/go/1.6/libexec"
   GOTOOLDIR="/usr/local/Cellar/go/1.6/libexec/pkg/tool/darwin_amd64"
   GO15VENDOREXPERIMENT="1"
   CC="clang"
   GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fno-common"
   CXX="clang++"
   CGO_ENABLED="1"
3. What did you do?
   If possible, provide a recipe for reproducing the error.
   A complete runnable program is good.
   A link on play.golang.org is best.

import (
        "encoding/json"
        "time"
        "os"
)


type Response struct {
        Name     string    `json:"name,omitempty"`
        Counter  int       `json:"counter,omitempty"`
        CreateAt time.Time `json:"createat,omitempty"`
}


func main() {
        var r Response

        enc := json.NewEncoder(os.Stdout)
        enc.Encode(r)
}

1. What did you expect to see?

Seems the expected result should be "{}" because the field createat is empty with ZERO value.

1. What did you see instead?

The above code will output:

   {"createat":"0001-01-01T00:00:00Z"}

[bradfitz]

Dup of #4357, etc