Extends and trigger together in CI/CD definition

We discovered that it is currently not supported to use trigger along with extends (as a list).

Example, using the shadowed jobs :

.foo:
  except:
    variables:
      - $FOO == "foo"
.bar:
  only:
    refs:
      - bar

This works:

thejob:
  extends:
    - .foo
    - .bar
  script:
    - echo "foo bar"

But this doesn't:

thejob:
  extends:
    - .foo
    - .bar
  trigger:
    project: mySuper/repo

Saying that jobs:thejob extends should be a string