Newbie Parent Child Question

I would like to use the parent-child pipe feature for several projects in a mono repo.

Each project has its own .git-ci.yml and the parent YML references this. This approach can be found in many examples:

maven-versioning-extension:
  trigger:
    include: bs-portal/bsp-project/bsp-build/trunk/maven-build-extensions/akdb-version-extension/.gitlab/ci.yml
    strategy: depend

maven-delivery-extension:
  trigger:
    include: bs-portal/bsp-project/bsp-build/trunk/maven-build-extensions/delivery-maven-extension/.gitlab/ci.yml
    strategy: depend

If I push changes in a way that does not fit a child pipeline, I get the error:

downstream pipeline can not be created, no staged / jobs for this pipeline

For example, a child pipeline looks like this:

extension-versioning-build:
  image: maven:3.8.3-openjdk-8-slim
  stage: build
  rules:
    - if: $CI_COMMIT_TAG
      when: never
    - if: '$CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH'
      changes:
      - bs-portal/bsp-project/bsp-build/trunk/maven-build-extensions/delivery-maven-extension/**/*
  script:
    - mvn $MAVEN_CLI_OPTS clean deploy -f bs-portal/bsp-project/bsp-build/trunk/maven-build-extensions/delivery-maven-extension/pom.xml -Dmaven.test.skip=true

It is correct that the child pipeline has no jobs because the rules enforce it. But I’m thinking wrong somewhere, because a search for this error message in connection with Monorepo returns no hits.

Applying the rules of the child pipeline to the parent pipeline shouldn’t be the solution, but currently I would use the workaround.

What I would like to achieve is that child pipelines that do not match are ignored.

Thanks for tips.

Regards
Torsten