Populate default values for optional keys in query parameters

[dzhus]

If the schema of :query parameters is a :map with {:optional keys that have default values set for them, there seems to be no way to enable add-optional-keys option for the default-value-transformer in the default chain.
This means there's no way to both use reitit coercion, have optional query parameters, and also populate default values for them (+ communicate those defaults via OpenAPI spec).

Is this by design/intentional?

As an example, a failing test is something like this:

(testing "default values for optional query params missing from request"
    (let [router (r/router ["/test"
                            {:name ::route
                             :coercion reitit.coercion.malli/coercion
                             :parameters {:query [:map
                                                  [:x {:optional true} ;;;; !!!!!
                                                   [:keyword {:default :a}]]]}}] ;;;;; <<<<<<
                           {:compile coercion/compile-request-coercers})]
      (is (= {:query {:x :a}}
             (-> (r/match-by-path router "/test")
                 (assoc :query-params {})
                 (coercion/coerce!))))))

Which as seen here fails with

FAIL in reitit.coercion-test/match->path-parameter-coercion-test (coercion_test.cljc:233)
default values for optional query params missing from request
expected: {:query {:x :a}}
  actual: {:query {}}

It seems to be fixable via custom middleware / coercion but I wonder if there'd be an issue with simply threading through options from :coercion to the default-value-transformer, which would then allow the API user to enable population of optional keys?