If a user sets the following configuration, I would expect a configuration error to be returned:

I think it should return an error today.

Its a question of when the error should be returned. Today, a blank / empty string is a valid entry in propagator.composite, but when create is called it doesn't find any propagator called with blank / empty name and produces an error.

By adding an additional JSON schema constraint around the length, we arguably shift the error generation to when parse is called.

I say "arguably" because there's no consistency in how JSON schema tooling works. Some, like the tooling we use in opentelemetry-java, is great for generating bindings from the schema, but doesn't attempt to enforce the validation. So we implement all the validation when interpreting the in-memory model in create. But a language with JSON schema tooling which better incorporates the validation keywords might be able to produce an error in parse.