[BUG] Presence of path parameter in parent reference triggers NPE while processing examples

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator?
• 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?
  • Expected: code is generated without any issues
  • Actual: a NullPointerException is thrown during generation
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

After upgrading from v7.12.0 to v7.13.0 of openapi-generator-cli code generation of one of our OpenAPIs throws the following exception:

Exception: Cannot invoke "java.util.Map.get(Object)" because "actualComponentsExamples" is null
        at org.openapitools.codegen.DefaultGenerator.processOperation(DefaultGenerator.java:1606)
        at org.openapitools.codegen.DefaultGenerator.processPaths(DefaultGenerator.java:1474)
        at org.openapitools.codegen.DefaultGenerator.generateApis(DefaultGenerator.java:663)
        at org.openapitools.codegen.DefaultGenerator.generate(DefaultGenerator.java:1296)
        at org.openapitools.codegen.cmd.Generate.execute(Generate.java:535)
        at org.openapitools.codegen.cmd.OpenApiGeneratorCommand.run(OpenApiGeneratorCommand.java:32)
        at org.openapitools.codegen.OpenAPIGenerator.main(OpenAPIGenerator.java:66)
Caused by: java.lang.NullPointerException: Cannot invoke "java.util.Map.get(Object)" because "actualComponentsExamples" is null
        at org.openapitools.codegen.utils.ExamplesUtils.unaliasExamples(ExamplesUtils.java:75)
        at org.openapitools.codegen.DefaultCodegen.unaliasExamples(DefaultCodegen.java:2355)
        at org.openapitools.codegen.DefaultCodegen.fromResponse(DefaultCodegen.java:5028)
        at org.openapitools.codegen.DefaultCodegen.fromOperation(DefaultCodegen.java:4685)
        at org.openapitools.codegen.languages.AbstractJavaCodegen.fromOperation(AbstractJavaCodegen.java:2225)
        at org.openapitools.codegen.DefaultGenerator.processOperation(DefaultGenerator.java:1574)
        ... 6 more

It's not related to a particular spec, I've tested with 2 different languages (jaxrs-spec and go) and both gave the same exception. While creating the reproducer I noticed that removing the path parameter from the operation path, and thus also from its reference, made the NPE disappear:

So the following throws the NPE:

  /reproducers/{id}:
    $ref: "operations.yaml#/paths/~1reproducers~1{id}"

but this doesn't:

  /reproducers:
    $ref: "operations.yaml#/paths/~1reproducers"

openapi-generator version

• NOK: v7.13.0
• OK: v7.12.0

OpenAPI declaration file content or url

https://gist.github.com/clone1612/e9ca124ca323843d0175c67a4890d5ee

Generation Details

docker run --rm -v "${PWD}:/local" openapitools/openapi-generator-cli:latest generate -i /local/reproducer.yaml -g jaxrs-spec -o /local/out/jaxrs-spec      

Steps to reproduce

1. Check out the linked gist and make sure all 3 files are located within the same directory
2. Run the docker cli command

Related issues/PRs

The ExampleUtils class that throws the NPE was introduced in #20933 so might be related to that PR

Suggest a fix

/

Start with org.openapitools.codegen.utils.ExamplesUtils.java at the reported line 75, then trace the calls through DefaultCodegen and DefaultGenerator.processOperation. Reproduce with the linked gist and the Docker CLI command using a path parameter in the referenced operation, and compare v7.12.0 with v7.13.0. Done means generation completes for both the parameterized and non-parameterized references without the reported NullPointerException.