add some sanity checks in ContentAwareFactory

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

i think it makes sense to add these checks to help the user debug what is going on. if the behaviour is extended in an application, this will already have happened outside this class.