[BUG][OCaml] Generated Docker API build fails with missing argument

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?

Description

The generated OCaml bindings to Docker Engine API cannot be build due to a missing argument. This is a re-open of the last error reported in #9787 for visibility.

File "src/apis/plugin_api.ml", line 22, characters 52-56:
22 |     Cohttp_lwt_unix.Client.call `POST uri ~headers ~body >>= fun (resp, body) ->
                                                         ^^^^
Error: This expression has type 'a -> Cohttp_lwt.Body.t
       but an expression was expected of type Cohttp_lwt.Body.t

comes from here:

{{#bodyParams}}
    let body = Request.{{#isFreeFormObject}}write_json_body{{/isFreeFormObject}}{{#isByteArray}}write_string_body{{/isByteArray}}{{^isFreeFormObject}}{{^isByteArray}}write_as_json_body{{/isByteArray}}{{/isFreeFormObject}} {{> to_json}} {{{paramName}}} in
{{/bodyParams}}

openapi-generator version

openapi-generator-cli 6.1.0-SNAPSHOT
  commit : 97daba5
  built  : 2022-07-04T07:33:51Z

OpenAPI declaration file content or url

https://docs.docker.com/engine/api/v1.41.yaml

Steps to reproduce

docker run --rm -v "${PWD}:/local" openapitools/openapi-generator-cli generate \
    -i https://docs.docker.com/engine/api/v1.41.yaml \
    -g ocaml \
    -o /local
sudo chown -R "$(whoami):$(whoami)" .
opam exec -- dune build @all

Related issues/PRs

• https://github.com/OpenAPITools/openapi-generator/issues/9787

Suggest a fix

The generated code is missing one argument, the converter to Yojson.Safe.t, which is probably the identity function in this case (fun x -> x).

let body = Request.write_as_json_body  input_stream in
Cohttp_lwt_unix.Client.call `POST uri ~headers ~body >>= fun (resp, body) ->

cc @wing328

Inspect modules/openapi-generator/src/main/resources/ocaml/api-impl.mustache, especially the body parameter rendering shown in the issue. Reproduce generation from the Docker Engine API v1.41.yaml and run opam exec -- dune build @all; done means the generated OCaml client builds without the missing-argument error.