You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: well_known_types.go
    path of file: ./repos/zeebe/clients/go/vendor/google.golang.org/protobuf/encoding/protojson
    
    the code of the file until where you have to start completion: // Copyright 2019 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package protojson

import (
	"bytes"
	"fmt"
	"math"
	"strconv"
	"strings"
	"time"

	"google.golang.org/protobuf/internal/encoding/json"
	"google.golang.org/protobuf/internal/errors"
	"google.golang.org/protobuf/internal/genid"
	"google.golang.org/protobuf/internal/strs"
	"google.golang.org/protobuf/proto"
	"google
    
func (d decoder) unmarshalAnyValue(unmarshal unmarshalFunc, m protoreflect.Message) error {
	// Skip ObjectOpen, and start reading the fields.
	d.Read()

	var found bool // Used for detecting duplicate "value".
	for {
		tok, err := d.Read()
		if err != nil {
			return err
		}
		switch tok.Kind() {
		case json.ObjectClose:
			if !found {
				return d.newError(tok.Pos(), `missing "value" field`)
			}
			return nil

		case json.Name:
			switch tok.Name() {
			case "@type":
				// Skip the value as this was previously parsed already.
				d.Read()

			case "value":
				if found {
					return d.newError(tok.Pos(), `duplicate "value" field`)
				}
				// Unmarshal the field value into the given message.
				if err := unmarshal(d, m); err != nil {
					return err
				}
				found = true

			default:
				if d.opts.DiscardUnknown {
					if err := d.skipJSONValue(); err != nil {
						return err
					}
					continue
				}
				return d.newError(tok.Pos(), "unknown field %v", tok.RawString())
			}
		}
	}
}