How to run docker build from pipeline

I have the following “shared.gitlab-ci.yml”:

############################################
# gfuchs/shared-pipeline
# 
# 
############################################

variables:
  GIT_SUBMODULE_STRATEGY: recursive
  DOCKERFILE_BUILD: docker/build/Dockerfile
  DOCKERFILE_TEST: docker/test/Dockerfile
  DOCKERFILE_ANALYZE: docker/analyze/Dockerfile
  BUILD_NAME: $CI_PROJECT_PATH_SLUG:$CI_COMMIT_REF_NAME-$CI_COMMIT_SHORT_SHA
  PREPARE_SCRIPT: ""
  BUILD_ARGS: ""

stages:
- build
- test
- analyze

before_script:
  - echo "Project Details:"
  - echo $CI_PROJECT_PATH_SLUG
  - echo $CI_COMMIT_REF_NAME
  - echo $CI_COMMIT_SHORT_SHA
  - echo "Build Variables:"
  - echo $BUILD_NAME
  - echo $DOCKERFILE_BUILD
  - echo $DOCKERFILE_TEST
  - echo $DOCKERFILE_ANALYZE
  - echo "Directory:"
  - ls -la
  - echo "Registry info:"
  - echo $CI_REGISTRY
  - echo $CI_REGISTRY_NAME
  - echo $CI_REGISTRY_USER
  - docker login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" $CI_REGISTRY
  - docker info

docker-build:
  image: docker:latest
  stage: build
  services:
    - docker:dind
  script:
    - docker build \
      --rm \
      -f $DOCKERFILE_BUILD \
      --build-arg BRANCH_NAME=$CI_COMMIT_REF_NAME \
      --build-arg BUILD_ARGS=$BUILD_ARGS \
      -t $BUILD_NAME
    - docker push $BUILD_NAME
  #rules:
  #  - exists:
  #      - $DOCKERFILE_BUILD

which I want to define for several projects. I have in another repo where my code is the following “gitlab-ci.yml”

#################################
# gfuchs-projects/action-mmo/black-knights
# Type: Unity Game
#################################
include:
  - project: gfuchs-projects/shared-pipeline
    ref: master
    file: shared.gitlab-ci.yml

In this repo I also do contain the “Dockerfile” in “./docker/build/Dockerfile”

FROM unityci/editor:windows-2020.1.16f1-base-0.17.2 as unity 
ARG BRANCH_NAME
ARG BUILD_ARGS
CMD echo "Hello world! This is my first Docker image. Branch: $BRANCH_NAME"

When I now build the pipeline I get the following output:

Initialized empty Git repository in /builds/gfuchs-projects/action-mmo/black-knights/.git/
Created fresh repository.
Checking out 3731ab28 as develop...
Updating/initializing submodules recursively...
Executing "step_script" stage of the job script
00:02
Using docker image sha256:6816f070b2395d750ce78e4fbdb7e9df0af63b7686f3063c09e008c2ef1a0036 for docker:latest with digest docker@sha256:9e13118c8f7b17349e2d350806082fdda135ebf2923376821f3eac23559b9141 ...
$ echo "Project Details:"
Project Details:
$ echo $CI_PROJECT_PATH_SLUG
gfuchs-projects-action-mmo-black-knights
$ echo $CI_COMMIT_REF_NAME
develop
$ echo $CI_COMMIT_SHORT_SHA
3731ab28
$ echo "Build Variables:"
Build Variables:
$ echo $BUILD_NAME
gfuchs-projects-action-mmo-black-knights:develop-3731ab28
$ echo $DOCKERFILE_BUILD
docker/build/Dockerfile
$ echo $DOCKERFILE_TEST
docker/test/Dockerfile
$ echo $DOCKERFILE_ANALYZE
docker/analyze/Dockerfile
$ echo "Directory:"
Directory:
$ ls -la
total 68
drwxrwxrwx    8 root     root          4096 Mar 14 20:43 .
drwxrwxrwx    4 root     root          4096 Mar 14 20:43 ..
-rw-rw-rw-    1 root     root          1509 Mar 14 20:43 .atomignore
drwxrwxrwx    7 root     root          4096 Mar 14 20:44 .git
-rw-rw-rw-    1 root     root          1848 Mar 14 20:43 .gitattributes
-rw-rw-rw-    1 root     root          1817 Mar 14 20:43 .gitignore
-rw-rw-rw-    1 root     root           230 Mar 14 20:43 .gitlab-ci.yml
drwxrwxrwx   13 root     root          4096 Mar 14 20:43 Assets
drwxrwxrwx    2 root     root          4096 Mar 14 20:43 Packages
drwxrwxrwx    2 root     root          4096 Mar 14 20:43 ProjectSettings
-rw-rw-rw-    1 root     root         11542 Mar 14 20:43 README.md
-rw-rw-rw-    1 root     root           947 Mar 14 20:43 Unity_lic.alf
-rw-rw-rw-    1 root     root          2485 Mar 14 20:43 Unity_v2017.x.ulf
drwxrwxrwx    3 root     root          4096 Mar 14 20:43 ci
drwxrwxrwx    3 root     root          4096 Mar 14 20:43 docker
$ echo "Registry info:"
Registry info:
$ echo $CI_REGISTRY
registry.gitlab.com
$ echo $CI_REGISTRY_NAME
$ echo $CI_REGISTRY_USER
gitlab-ci-token
$ docker login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" $CI_REGISTRY
WARNING! Using --password via the CLI is insecure. Use --password-stdin.
WARNING! Your password will be stored unencrypted in /root/.docker/config.json.
Configure a credential helper to remove this warning. See
https://docs.docker.com/engine/reference/commandline/login/#credentials-store
Login Succeeded
$ docker info
Client:
 Context:    default
 Debug Mode: false
Server:
 Containers: 0
  Running: 0
  Paused: 0
  Stopped: 0
 Images: 0
 Server Version: 20.10.13
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  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 io.containerd.runtime.v1.linux runc
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: 2a1d4dbdb2a1030dc5b01e96fb110a9d9f150ecc
 runc version: v1.0.3-0-gf46b6ba2
 init version: de40ad0
 Security Options:
  apparmor
  seccomp
   Profile: default
 Kernel Version: 5.4.109+
WARNING: API is accessible on http://0.0.0.0:2375 without encryption.
         Access to the remote API is equivalent to root access on the host. Refer
         to the 'Docker daemon attack surface' section in the documentation for
         more information: https://docs.docker.com/go/attack-surface/
 Operating System: Alpine Linux v3.15 (containerized)
 OSType: linux
 Architecture: x86_64
 CPUs: 1
 Total Memory: 3.599GiB
 Name: 2081a7d65bb1
 ID: V7MM:NOII:G6SB:JNWS:TMSU:HAM7:HFVR:OW72:33S5:JRRT:QJXN:V5OJ
 Docker Root Dir: /var/lib/docker
 Debug Mode: false
 Registry: https://index.docker.io/v1/
 Labels:
 Experimental: false
 Insecure Registries:
  127.0.0.0/8
 Live Restore Enabled: false
 Product License: Community Engine
$ docker build \ --rm \ -f $DOCKERFILE_BUILD \ --build-arg BRANCH_NAME=$CI_COMMIT_REF_NAME \ --build-arg BUILD_ARGS=$BUILD_ARGS \ -t $BUILD_NAME
"docker build" requires exactly 1 argument.
See 'docker build --help'.
Usage:  docker build [OPTIONS] PATH | URL | -
Build an image from a Dockerfile
Cleaning up project directory and file based variables
00:01
ERROR: Job failed: exit code 1

It seems the “docker build” command is wrong and I tried literally anything but it won’t work. How do I accomplish that the “docker build” works?