[BUG] Parsing fails for OpenAPI schema referenced multiple times

Start by running the parser against packages/openapi-schema-parser/test/documents/valid-asyncapi3.yaml, as described in the reproduction steps. Inspect the OpenAPI schema parser dependency and its existing tests to confirm the repeated-reference failure. Done means the document parses without InvalidTypeError and all OpenAPI 3.0 schemas load correctly.

Describe the bug.

An InvalidTypeError is thrown during document parsing of a valid OpenAPI 3.0 schema which uses nullable: true, even though schemaFormat was set correctly.

The error only occurs in some circumstances when a schema is referenced multiple times.

I previously reported this as https://github.com/asyncapi/openapi-schema-parser/issues/275 before the move of the openapi-schema-parser component.

The transformation of OpenAPI Schema to JSON Schema using the @openapi-contrib/openapi-schema-to-json-schema library, modifies the input OpenAPI Schema. This triggers the error when the same schema is transformed for a second time. This seems to be a bug in this version of the library; it occurs even though the cloneSchema parameter is set to true.

For the first reference, the schema with nullable gets correctly transformed from OpenAPI Schema:

type: ["string"] , nullable: true

to Json Schema:

type: ["string", "null"]

When it is then parsed again (because the same schema is also referenced from another location), the transformation fails with the InvalidTypeError because it doesn't expect a type with an array as value in an OpenAPI 3.0 Schema.

If this issue is accepted, I can create a pull request to update the @openapi-contrib/openapi-schema-to-json-schema dependency, which I verified fixes the issue (code is in this branch. I first tried a structuredClone on the input schema, but that didn't fix all occurrences of the issue.

Expected behavior

AsyncAPI being parsed without error, with all OpenAPI 3.0 schemas correctly loaded.

Screenshots

How to Reproduce

1. Load this asyncapi document in AsyncAPI studio, or run the parser directly on it
2. This will result in an InvalidTypeError

🖥️ Device Information [optional]

• Operating System (OS): Windows 11
• Browser: Edge
• Browser Version: 153

👀 Have you checked for similar open issues?

• I checked and didn't find similar issue

🏢 Have you read the Contributing Guidelines?

• I have read the Contributing Guidelines

Are you willing to work on this issue ?

Yes I am willing to submit a PR!