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• 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?
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• What's the actual output vs expected output?
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Description

If a schema contains additionalProperties: true, that is supposed to be equivalent to additionalProperties: {}, which implies that arbitrary properties of ANY type (string, integer, object, etc.) may be added to the object/class/struct that is generated for that schema.
However, ModelUtils.getAdditionalProperties() will return an instance of ObjectSchema in this case rather than an instance of Schema. This would be equivalent to a schema with this value for the additionalProperties field:

  additionalProperties:
    type: object

This would imply that arbitrary properties added to the object/class/struct for that schema should be an "object" (i.e. Map<String,Object> in Java, map[string]interface{} in Go, etc.).

openapi-generator version

This was observed in an old version of the project (3.3.3) and is still present in the latest from the master branch.

OpenAPI declaration file content or url

Generation Details

Steps to reproduce

Related issues/PRs

Suggest a fix

Modify ModelUtils.getAdditionalProperties() so that it returns an instance of Schema instead of ObjectSchema in the scenario where additionalProperties: true is detected.