attributevalue behaves different from dynamodbattribute with omitemptyelem on maps

[curquhart]

Acknowledgements

• [x] I have searched (https://github.com/aws/aws-sdk/issues?q=is%3Aissue) for past instances of this issue
• [x] I have verified all of my SDK modules are up-to-date (you can perform a bulk update with go get -u github.com/aws/aws-sdk-go-v2/...)

Describe the bug

omitemptyelem does not omit empty maps from the dynamo attribute map. This differs from the sdk v1 functionality and can cause problems with constraints.

Regression Issue

• [ ] Select this option if this issue appears to be a regression.

Expected Behavior

I would expect the map field (see sample code) to be omitted

Current Behavior

The map field (see sample code) is omitted by dynamodbattribute (sdk v1) but included by attributevalue (sdk v2)

Reproduction Steps

Sample code:

package main

import (
	"github.com/aws/aws-sdk-go-v2/feature/dynamodb/attributevalue"
	"github.com/aws/aws-sdk-go/service/dynamodb/dynamodbattribute"
)

type Record struct {
	M map[string]string `dynamodbav:"map,omitempty,omitemptyelem"`
}

func main() {
	mm1, err := dynamodbattribute.MarshalMap(&Record{
		M: make(map[string]string),
	})
	if err != nil {
		panic(err)
	}
	println("dynamodbattribute")
	for key := range mm1 {
		println(key)
	}

	mm2, err := attributevalue.MarshalMap(&Record{
		M: make(map[string]string),
	})
	if err != nil {
		panic(err)
	}
	println("attributevalue")
	for key := range mm2 {
		println(key)
	}
}

Output:

dynamodbattribute
attributevalue
map

Possible Solution

No response

Additional Information/Context

I don't know if this is actually an issue; I recognize this could be an intentional breaking change between SDK versions (since technically, an empty map is not a zero value), but I wanted to create this issue because even if it's not an issue, it could help identify it for other people migrating to the new SDK version.

AWS Go SDK V2 Module Versions Used

github.com/aws/aws-sdk-go v1.55.7
github.com/aws/aws-sdk-go-v2/feature/dynamodb/attributevalue v1.19.3
github.com/aws/aws-sdk-go-v2/service/dynamodb v1.43.4 // indirect
github.com/aws/aws-sdk-go-v2/service/dynamodbstreams v1.25.6 // indirect
github.com/aws/smithy-go v1.22.4 // indirect

Compiler and Version used

go version go1.24.0 darwin/arm64

Operating System and version

macos 15.5