[BUG] cannot implement isEmpty() in java.util.Map; return type java.lang.Boolean is not compatible with boolean

I am using maven openapi generator plugin version 6.0.0. Here is the sample project https://github.com/pc-vkotecha/openapi_demo

I have an api where requrest type and response type is a class which extends HashMap or implements Map, it is not able to parse that model and throws the exception like this

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.10.1:compile (default-compile) on project demo: Compilation failure
[ERROR] /home/vkotecha/source_code/openapi_demo/demo/target/generated-sources/openapi/src/main/java/org/openapitools/client/model/Response.java:[59,18] isEmpty() in org.openapitools.client.model.Response cannot implement isEmpty() in java.util.Map
[ERROR]   return type java.lang.Boolean is not compatible with boolean

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?
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Description

openapi-generator version

I am using maven openapi generator plugin version 6.0.0.

OpenAPI declaration file content or url

Here it is: https://github.com/pc-vkotecha/openapi_demo/blob/main/api-docs.json

Generation Details

Steps to reproduce

1. git clone https://github.com/pc-vkotecha/openapi_demo
2. cd demo
3. mvn clean install

Related issues/PRs

Suggest a fix

Clone the linked openapi_demo project, review api-docs.json, and run mvn clean install from demo to reproduce the failure in generated-sources/openapi/src/main/java/org/openapitools/client/model/Response.java. Trace how the Java model is generated for a class extending HashMap or implementing Map, then verify that the generated project compiles successfully.