[BUG][SCALA-AKKA] Doesn't generate models when defined inline (reproduced for java & scala-akka)

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? No models generated vs models generated
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

Running java -jar openapi-generator-cli.jar generate -i 'swagger.json' -g scala-akka -o scala_client --generate-alias-as-model (also without config and/or without --generate-alias-as-model), doesn't produce any model libs.

Removing "additionalProperties": false, from the inline schema def makes it generate model classes. What also works is to define the schema using definitions + "$ref" : "..." - but that's not really feasible with the library I'm using for my server.

openapi-generator version

5.0.1 and also tested with openapi-generator-cli-5.1.0-20210304.083949-99.jar

OpenAPI declaration file content or url

swagger.json gist

Generation Details

X

Steps to reproduce

Just run java -jar openapi-generator-cli.jar generate -i 'swagger.json' -g scala-akka -o scala_client where swagger.json is the file I linked above, and the jar is either 5.0.1 or the snapshot version I mentioned.

Related issues/PRs

X

Suggest a fix

Somehow removing "additionalProperties": false, from the inline schema def makes it generate model classes. Setting it to true doesn't help either (not sure true is valid though). Referencing it with "$ref": "..." and moving the schema to definitions also solves this (but I can't use that solution due to the. lib I'm using).

Start by running the documented openapi-generator command with the linked swagger.json gist and compare generation with an inline schema containing additionalProperties: false. Trace the scala-akka model-generation path, then verify that models are generated for the reproduced case and add a regression test if the relevant test location is identified.