[BUG][JAVA][spring-mvc] Generated Code for Map of Maps Return Type does not compile

[emileonhardt]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Bounty to sponsor the fix (example)

Description

The Java-Code (spring-mvc) generated from OpenAPI-YAML for a Map of Maps ist not syntactically correct:
Actual:
ResponseEntity<Map<String, Map<String>>
Expected:
ResponseEntity<Map<String, Map<String,String>>

Gradle v6.1.1.

openapi-generator version

4.2.3
4.2.2
(Was working in 4.0.3)

OpenAPI declaration file content or url

See https://gist.github.com/emileonhardt/3cc234261af6af8cc55f4267ae56bc9a

Command line used for generation

gradle openApiGenerate

Steps to reproduce

gradle clean openApiGenerate

Related issues/PRs

Nothing so far.

Suggest a fix

None known.