Should dropshot endpoints be able to return `Option<T>`?

Today, these two endpoints:

#[endpoint {
    method = GET,
    path = "/foo",
}]
async fn get_foo(_rqctx: RequestContext<()>) -> Result<HttpResponseOk<Foo>, HttpError> { .. }

#[endpoint {
    method = GET,
    path = "/option_foo",
}]
async fn get_option_foo(_rqctx: RequestContext<()>) -> Result<HttpResponseOk<Option<Foo>>, HttpError> { .. }

produce identical OpenAPI definitions:

    "/foo": {
      "get": {
        "operationId": "get_foo",
        "responses": {
          "200": {
            "description": "successful operation",
            "content": {
              "application/json": {
                "schema": {
                  "$ref": "#/components/schemas/Foo"
                }
              }
            }
          },
          "4XX": {
            "$ref": "#/components/responses/Error"
          },
          "5XX": {
            "$ref": "#/components/responses/Error"
          }
        }
      }
    },
    "/option_foo": {
      "get": {
        "operationId": "get_option_foo",
        "responses": {
          "200": {
            "description": "successful operation",
            "content": {
              "application/json": {
                "schema": {
                  "$ref": "#/components/schemas/Foo"
                }
              }
            }
          },
          "4XX": {
            "$ref": "#/components/responses/Error"
          },
          "5XX": {
            "$ref": "#/components/responses/Error"
          }
        }
      }
    }
  },

This is surprising/wrong, and causes generated clients to not realize that get_option_foo() might return None / null instead of a Foo. It's relatively easy to work around this by returning a struct that contains an Option. I don't know if returning an Option directly should work; if not, could we reject it at compile time somehow?

Start by tracing how endpoint return types are converted into OpenAPI response schemas, using the /foo and /option_foo examples as the comparison. Determine and test the intended behavior for direct Option returns, then verify that the generated schema reflects nullability or that unsupported returns are rejected at compile time.