gitlab-rails: "500 Internal Server Error" when linting malformed .gitlab-ci.yml

the yaml file below breaks linting:

stages:
    - npm-build
    - mvn-build

job-npm-build:
    stage: npm-build
    image: node:12.13.1
    script:
        - cd web/foobar
        - npm install
        - npm run build
    artifacts:
        - web/foobar/build

job-mvn-build:
    stage: mvn-build
    image: maven:3.6.3-jdk-8
    script:
        - cd parent
        - mvn clean package

Our up2date on premise installation as well as my test project here on https://gitlab.com/udotirol/the-test-project/pipelines/102866092 shows an "undefined error" in the UI and on premise, our production.log contains this:

Started POST "/foobar/foobar/-/ci/lint" for 10.10.9.1 at 2019-12-13 12:03:24 +0100
Processing by Projects::Ci::LintsController#create as HTML
  Parameters: {"utf8"=>"✓", "authenticity_token"=>"[FILTERED]", "content"=>"[FILTERED]", "namespace_id"=>"foobar", "project_id"=>"foobar"}
Completed 500 Internal Server Error in 66ms (ActiveRecord: 6.1ms | Elasticsearch: 0.0ms)

TypeError (no implicit conversion of Symbol into Integer):

lib/gitlab/ci/config/entry/artifacts.rb:57:in `expose_as_present?'
lib/gitlab/config/entry/validatable.rb:20:in `validate'
lib/gitlab/config/entry/validatable.rb:11:in `block in included'
lib/gitlab/config/entry/node.rb:23:in `instance_exec'
lib/gitlab/config/entry/node.rb:23:in `block in initialize'
lib/gitlab/config/entry/node.rb:22:in `each'
lib/gitlab/config/entry/node.rb:22:in `initialize'

The issue with the YAML file is that the "artifacts" keyword lacks the "paths" keyword as a child, so the correct version would be

    artifacts:
      paths:
        - web/foobar/build