Ballerina OpenAPI sanitize is not working for the type names used with the array

Description:

The --use-sanitized-oas option is not working with the type reference name used as a member of an array schema. Currently the generation failed with the NPE. But the root cause is the sanitisation.

Identified from: https://github.com/ballerina-platform/ballerina-library/issues/6906

Steps to reproduce:

Please use the following OpenAPI specification to reproduce the issue:

openapi: 3.0.1
info:
  title: Api
  version: 0.1.0
servers:
- url: "{server}:{port}/api"
  variables:
    server:
      default: http://localhost
    port:
      default: "9999"
paths:
  /albums:
    get:
      operationId: getAlbums
      description: Get albums by genre
      parameters:
      - name: genre
        in: query
        required: true
        description: Album genre
        schema:
          type: string
      - name: API-VERSION
        in: header
        description: API Version
        schema:
          $ref: '#/components/schemas/VERSION'
          default: V1
      responses:
        "200":
          description: Albums found
          headers:
            req-id:
              required: true
              description: Request ID
              schema:
                type: integer
                format: int64
            api-version:
              required: true
              description: API Version
              schema:
                type: string
            session-id:
              required: true
              description: Session ID
              schema:
                type: string
          content:
            application/json:
              schema:
                type: array
                items:
                  $ref: '#/components/schemas/album'
components:
  schemas:
    album:
      required:
      - artist
      - genre
      - id
      - name
      type: object
      properties:
        id:
          type: string
          description: Album ID
        name:
          type: string
          description: Album name
        artist:
          type: string
          description: Album artist
        genre:
          type: string
          description: Album genre
      additionalProperties: false
    VERSION:
      type: string
      description: API Version
      enum:
      - V1
      - V2

$ bal openapi -i openapi.yaml --mode client --use-sanitize-oas

ballerina: Oh no, something really went wrong. Bad. Sad.

We appreciate it if you can report the code that broke Ballerina in
https://github.com/ballerina-platform/ballerina-lang/issues with the
log you get below and your sample code.

We thank you for helping make us better.

[2024-08-26 13:28:42,213] SEVERE {b7a.log.crash} - Cannot invoke "io.swagger.v3.oas.models.media.Schema.get$ref()" because "schemaValue" is null 
java.lang.NullPointerException: Cannot invoke "io.swagger.v3.oas.models.media.Schema.get$ref()" because "schemaValue" is null
        at io.ballerina.openapi.core.generators.type.TypeGeneratorUtils.getTypeGenerator(TypeGeneratorUtils.java:67)
        at io.ballerina.openapi.core.generators.type.generators.ArrayTypeGenerator.getTypeDescNodeForArraySchema(ArrayTypeGenerator.java:176)
        at io.ballerina.openapi.core.generators.type.BallerinaTypesGenerator.generateTypeDescriptorNodeForOASSchema(BallerinaTypesGenerator.java:151)
        at io.ballerina.openapi.core.generators.type.BallerinaTypesGenerator.generateTypeDescriptorNodeForOASSchema(BallerinaTypesGenerator.java:88)
        at io.ballerina.openapi.core.generators.common.TypeHandler.getTypeNodeFromOASSchema(TypeHandler.java:196)
        at io.ballerina.openapi.core.generators.common.TypeHandler.getTypeNodeFromOASSchema(TypeHandler.java:191)
        at io.ballerina.openapi.core.generators.client.FunctionReturnTypeGeneratorImp.getDataType(FunctionReturnTypeGeneratorImp.java:188)
        at io.ballerina.openapi.core.generators.client.FunctionReturnTypeGeneratorImp.populateReturnType(FunctionReturnTypeGeneratorImp.java:135)
        at io.ballerina.openapi.core.generators.client.FunctionReturnTypeGeneratorImp.getReturnTypeInfo(FunctionReturnTypeGeneratorImp.java:113)
        at io.ballerina.openapi.core.generators.client.FunctionReturnTypeGeneratorImp.getReturnType(FunctionReturnTypeGeneratorImp.java:81)
        at io.ballerina.openapi.core.generators.client.ResourceFunctionSignatureGenerator.generateFunctionSignature(ResourceFunctionSignatureGenerator.java:86)
        at io.ballerina.openapi.core.generators.client.ResourceFunctionGenerator.generateFunction(ResourceFunctionGenerator.java:88)
        at io.ballerina.openapi.core.generators.client.BallerinaClientGenerator.addResourceFunction(BallerinaClientGenerator.java:653)
        at io.ballerina.openapi.core.generators.client.BallerinaClientGenerator.createResourceFunctions(BallerinaClientGenerator.java:643)
        at io.ballerina.openapi.core.generators.client.BallerinaClientGenerator.getClassDefinitionNode(BallerinaClientGenerator.java:260)
        at io.ballerina.openapi.core.generators.client.BallerinaClientGenerator.getModuleMemberDeclarationNodes(BallerinaClientGenerator.java:216)
        at io.ballerina.openapi.core.generators.client.BallerinaClientGenerator.getSyntaxTree(BallerinaClientGenerator.java:194)
        at io.ballerina.openapi.core.generators.client.BallerinaClientGenerator.generateSyntaxTree(BallerinaClientGenerator.java:188)
        at io.ballerina.openapi.cmd.BallerinaCodeGenerator.generateClientFiles(BallerinaCodeGenerator.java:439)
        at io.ballerina.openapi.cmd.BallerinaCodeGenerator.generateClient(BallerinaCodeGenerator.java:258)
        at io.ballerina.openapi.cmd.OpenApiCmd.generatesClientFile(OpenApiCmd.java:445)
        at io.ballerina.openapi.cmd.OpenApiCmd.openApiToBallerina(OpenApiCmd.java:368)
        at io.ballerina.openapi.cmd.OpenApiCmd.execute(OpenApiCmd.java:267)
        at java.base/java.util.Optional.ifPresent(Optional.java:178)
        at io.ballerina.cli.launcher.Main.main(Main.java:59)

Affected Versions:

Ballerina SwanLake Update 10(2201.10.x)

ballerina-platform / ballerina-library

Ballerina OpenAPI sanitize is not working for the type names used with the array #6919