docker stack config environment variable merge is not as expected

Description

Hey.
I want to use docker stack config to merge two docker compose files. In it I want to overwrite an environment variable with an empty value. However, this variable is not overwritten.

Reproduce

1. Create a docker-compose file as base with name main.yml

version: "3.8"
services:
  test:
    environment:
      TEST: "1"
      TEST_ENV: test_value

2. Create a docker-compose file with name override.yml as overwrite with a environment variable with empty value

version: "3.8"
services:
  test:
    environment:
      TEST_ENV: ''

3. Run docker stack config -c main.yml -c override.yml to merge the files
4. The output of the command is

version: "3.8"
services:
  test:
    environment:
      TEST: "1"
      TEST_ENV: test_value

Expected behavior

The output of docker stack config -c main.yml -c override.yml should be

version: '3.8'
services:
  test:
    environment:
      TEST: 1
      TEST_ENV: ''

docker version

Client: Docker Engine - Community
 Cloud integration: v1.0.35
 Version:           24.0.2
 API version:       1.43
 Go version:        go1.20.4
 Git commit:        cb74dfc
 Built:             Thu May 25 21:52:17 2023
 OS/Arch:           linux/amd64
 Context:           default

Server: Docker Desktop
 Engine:
  Version:          24.0.2
  API version:      1.43 (minimum version 1.12)
  Go version:       go1.20.4
  Git commit:       659604f
  Built:            Thu May 25 21:52:17 2023
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          1.6.21
  GitCommit:        3dce8eb055cbb6872793272b4f20ed16117344f8
 runc:
  Version:          1.1.7
  GitCommit:        v1.1.7-0-g860f061
 docker-init:
  Version:          0.19.0
  GitCommit:        de40ad0

docker info

Client: Docker Engine - Community
 Version:    24.0.2
 Context:    default
 Debug Mode: false
 Plugins:
  buildx: Docker Buildx (Docker Inc.)
    Version:  v0.11.0
    Path:     /usr/local/lib/docker/cli-plugins/docker-buildx
  compose: Docker Compose (Docker Inc.)
    Version:  v2.19.1
    Path:     /usr/local/lib/docker/cli-plugins/docker-compose
  dev: Docker Dev Environments (Docker Inc.)
    Version:  v0.1.0
    Path:     /usr/local/lib/docker/cli-plugins/docker-dev
  extension: Manages Docker extensions (Docker Inc.)
    Version:  v0.2.20
    Path:     /usr/local/lib/docker/cli-plugins/docker-extension
  init: Creates Docker-related starter files for your project (Docker Inc.)
    Version:  v0.1.0-beta.6
    Path:     /usr/local/lib/docker/cli-plugins/docker-init
  sbom: View the packaged-based Software Bill Of Materials (SBOM) for an image (Anchore Inc.)
    Version:  0.6.0
    Path:     /usr/local/lib/docker/cli-plugins/docker-sbom
  scan: Docker Scan (Docker Inc.)
    Version:  v0.26.0
    Path:     /usr/local/lib/docker/cli-plugins/docker-scan
  scout: Command line tool for Docker Scout (Docker Inc.)
    Version:  0.16.1
    Path:     /usr/local/lib/docker/cli-plugins/docker-scout

Server:
 Containers: 4
  Running: 0
  Paused: 0
  Stopped: 4
 Images: 40
 Server Version: 24.0.2
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Using metacopy: false
  Native Overlay Diff: true
  userxattr: false
 Logging Driver: json-file
 Cgroup Driver: cgroupfs
 Cgroup Version: 1
 Plugins:
  Volume: local
  Network: bridge host ipvlan macvlan null overlay
  Log: awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog
 Swarm: inactive
 Runtimes: io.containerd.runc.v2 runc
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: 3dce8eb055cbb6872793272b4f20ed16117344f8
 runc version: v1.1.7-0-g860f061
 init version: de40ad0
 Security Options:
  seccomp
   Profile: builtin
 Kernel Version: 5.15.90.1-microsoft-standard-WSL2
 Operating System: Docker Desktop
 OSType: linux
 Architecture: x86_64
 CPUs: 16
 Total Memory: 15.51GiB
 Name: docker-desktop
 ID: 12872eb9-0823-483b-8385-4dd8b84702a4
 Docker Root Dir: /var/lib/docker
 Debug Mode: false
 HTTP Proxy: http.docker.internal:3128
 HTTPS Proxy: http.docker.internal:3128
 No Proxy: hubproxy.docker.internal
 Experimental: false
 Insecure Registries:
  hubproxy.docker.internal:5555
  127.0.0.0/8
 Live Restore Enabled: false

WARNING: No blkio throttle.read_bps_device support
WARNING: No blkio throttle.write_bps_device support
WARNING: No blkio throttle.read_iops_device support
WARNING: No blkio throttle.write_iops_device support

Additional Info

I use Docker Desktop v4.21.1 on Windows 11. I run the command on Ubuntu via WSL 2

Start by reproducing the merge with main.yml and override.yml using docker stack config -c main.yml -c override.yml. Trace the docker stack config merge path in the Docker CLI and add coverage for an override environment variable set to an empty value. Done means the rendered configuration preserves TEST_ENV: '' instead of the base value.