Custom body parser issue

[krzykamil]

Moving this https://discourse.hanamirb.org/t/custom-body-parser-from-hanami-2-1-guides/929/4 to an issue, since I believe this is an error. Especially after testing a direct example from GETTING STARTED guide
https://guides.hanamirb.org/v2.1/actions/parameters/#body-parsers
https://github.com/hanami/router?tab=readme-ov-file#custom-parsers

Those two examples seem to be broken. I tested them and the error produced is as in the forum thread.
I've traced the error down to:

hanami-router-2.1.0/lib/hanami/middleware/body_parser/class_interface.rb:54

        def build_parsers(parser_specs, registry = {})
          return DEFAULT_BODY_PARSERS if parser_specs.empty?

And with the given examples, the error disappears when the custom parser is wrapped in an array, but obviously this is not the actual solution, since we would want to just pass an parser that handles a given format.

I would like to work on it if this is an actual bug, but would prefer to get a confirmation since I am not so sure about it.