Unable to load RELATIVE ref: ../../models/BadRequest.yaml path: /

Description

This works:

  responses:
    200:
      description: successful operation
      content:
        application/json:
          schema:
            $ref: '../../models/GetSessionListResponse.yaml'

This also work:

  responses:
    400:
      $ref: './openapi/models/BadRequest.yaml'

But this don't work:

  responses:
    400:
      $ref: '../../models/BadRequest.yaml'

19:09:07.732 [Thread-0] WARN  io.swagger.v3.parser.OpenAPIV3Parser - Exception while resolving:
java.lang.RuntimeException: Unable to load RELATIVE ref: ../../models/BadRequest.yaml path: /
        at io.swagger.v3.parser.util.RefUtils.readExternalRef(RefUtils.java:239)
        at io.swagger.v3.parser.ResolverCache.loadRef(ResolverCache.java:119)
        at io.swagger.v3.parser.processors.ExternalRefProcessor.processRefToExternalResponse(ExternalRefProcessor.java:344)
        at io.swagger.v3.parser.processors.ResponseProcessor.processReferenceResponse(ResponseProcessor.java:84)
        at io.swagger.v3.parser.processors.ResponseProcessor.processResponse(ResponseProcessor.java:41)
        at io.swagger.v3.parser.processors.OperationProcessor.processOperation(OperationProcessor.java:56)
        at io.swagger.v3.parser.processors.PathsProcessor.processPaths(PathsProcessor.java:84)
        at io.swagger.v3.parser.OpenAPIResolver.resolve(OpenAPIResolver.java:49)
        at io.swagger.v3.parser.OpenAPIV3Parser.resolve(OpenAPIV3Parser.java:172)
        at io.swagger.v3.parser.OpenAPIV3Parser.readContents(OpenAPIV3Parser.java:153)
        at io.swagger.v3.parser.OpenAPIV3Parser.readLocation(OpenAPIV3Parser.java:89)
        at io.swagger.parser.OpenAPIParser.readLocation(OpenAPIParser.java:16)
        at io.swagger.codegen.v3.config.CodegenConfigurator.toClientOptInput(CodegenConfigurator.java:517)
        at io.swagger.codegen.v3.cli.cmd.Generate.run(Generate.java:376)
        at java.base/java.lang.Thread.run(Thread.java:832)
Caused by: java.lang.RuntimeException: Could not find ../../models/BadRequest.yaml on the classpath
        at io.swagger.v3.parser.util.ClasspathHelper.loadFileFromClasspath(ClasspathHelper.java:31)
        at io.swagger.v3.parser.util.RefUtils.readExternalRef(RefUtils.java:233)
        ... 14 common frames omitted
19:09:07.737 [Thread-0] WARN  io.swagger.v3.parser.OpenAPIV3Parser - Exception while resolving:
java.lang.RuntimeException: Unable to load RELATIVE ref: ../../models/BadRequest.yaml path: /
        at io.swagger.v3.parser.util.RefUtils.readExternalRef(RefUtils.java:239)
        at io.swagger.v3.parser.ResolverCache.loadRef(ResolverCache.java:119)
        at io.swagger.v3.parser.processors.ExternalRefProcessor.processRefToExternalResponse(ExternalRefProcessor.java:344)
        at io.swagger.v3.parser.processors.ResponseProcessor.processReferenceResponse(ResponseProcessor.java:84)
        at io.swagger.v3.parser.processors.ResponseProcessor.processResponse(ResponseProcessor.java:41)
        at io.swagger.v3.parser.processors.OperationProcessor.processOperation(OperationProcessor.java:56)
        at io.swagger.v3.parser.processors.PathsProcessor.processPaths(PathsProcessor.java:84)
        at io.swagger.v3.parser.OpenAPIResolver.resolve(OpenAPIResolver.java:49)
        at io.swagger.v3.parser.OpenAPIV3Parser.resolve(OpenAPIV3Parser.java:172)
        at io.swagger.v3.parser.OpenAPIV3Parser.readContents(OpenAPIV3Parser.java:153)
        at io.swagger.v3.parser.OpenAPIV3Parser.readLocation(OpenAPIV3Parser.java:89)
        at io.swagger.parser.OpenAPIParser.readLocation(OpenAPIParser.java:16)
        at io.swagger.codegen.v3.config.CodegenConfigurator.toClientOptInput(CodegenConfigurator.java:526)
        at io.swagger.codegen.v3.cli.cmd.Generate.run(Generate.java:376)
        at java.base/java.lang.Thread.run(Thread.java:832)
Caused by: java.lang.RuntimeException: Could not find ../../models/BadRequest.yaml on the classpath
        at io.swagger.v3.parser.util.ClasspathHelper.loadFileFromClasspath(ClasspathHelper.java:31)
        at io.swagger.v3.parser.util.RefUtils.readExternalRef(RefUtils.java:233)
        ... 14 common frames omitted
Exception in thread "Thread-0" java.lang.NullPointerException: Cannot invoke "io.swagger.v3.oas.models.Components.getSchemas()" because the return value of "io.swagger.v3.oas.models.OpenAPI.getComponents()" is null
        at io.swagger.codegen.v3.DefaultGenerator.generateModels(DefaultGenerator.java:334)
        at io.swagger.codegen.v3.DefaultGenerator.generate(DefaultGenerator.java:779)
        at io.swagger.codegen.v3.cli.cmd.Generate.run(Generate.java:378)
        at java.base/java.lang.Thread.run(Thread.java:832)

Swagger-codegen version

swagger-codegen-cli-3.0.22.jar

Swagger declaration file content or url

openapi: 3.0.1

paths:
  /system/getSessionList:
    $ref: './openapi/paths/system/getSessionList.yaml'

paths/system/getSessionList.yaml:

get:
  tags:
  - system
  summary: Get session list
  description: Multiple values
  operationId: getSessionList
  responses:
    200:
      description: successful operation
      content:
        application/json:
          schema:
            $ref: '../../models/GetSessionListResponse.yaml'
    400:
      $ref: '../../models/BadRequest.yaml'

Command line used for generation

docker run --rm -v ${PWD}:/local -w /local openjdk java -jar swagger-codegen-cli.jar generate --input-spec /local/openapi.yaml --lang openapi-yaml --output /local/out/ -c /local/openapi-codegen-php.json

Steps to reproduce

Related issues/PRs

Suggest a fix/enhancement

Start with io.swagger.v3.parser.util.RefUtils.readExternalRef and the ClasspathHelper.loadFileFromClasspath failure shown in the stack trace, then trace how ResolverCache.loadRef handles the nested path. Reproduce with the supplied Docker command and YAML files. Done means the relative response reference resolves without warnings and generation does not end with the reported NullPointerException.