[BUG][JAVA] NullPointerException in getEnumValueForProperty when generating model with oneOf and discriminator

[Radenixlol]

Bug Report Checklist

openapi.yaml

[x] Have you provided a full/minimal spec to reproduce the issue?

[x] Have you validated the input using an OpenAPI validator?

[x] Have you tested with the latest master to confirm the issue still exists?

[x] Have you searched for related issues/PRs?

[x] What's the actual output vs expected output? (Actual: Crash. Expected: Generated code)

[ ] [Optional] Sponsorship to speed up the bug fix or feature request (example)

When generating a Java client, the generator fails with a NullPointerException while processing a specific model named 'Node'. This model uses a oneOf list combined with a discriminator (see spec below).

The error seems to originate in DefaultCodegen.getEnumValueForProperty (line ~3221), which is called by setEnumDiscriminatorDefaultValue. The root cause is a NullPointerException because var.allowableValues is null when the code attempts to call .get(Object) on it. This blocks the entire code generation process.

Stack Trace:

[main] WARN  o.o.codegen.DefaultCodegen - OpenAPI 3.1 support is still in beta. To report an issue related to 3.1 spec, please kindly open an issue in the Github repo: https://github.com/openAPITools/openapi-generator.
[main] INFO  o.o.codegen.DefaultGenerator - Model AnnotationsTrait not generated since it's a free-form object
Exception in thread "main" java.lang.RuntimeException: Could not process model 'Node'.Please make sure that your schema is correct!
        at org.openapitools.codegen.DefaultGenerator.generateModels(DefaultGenerator.java:518)
        at org.openapitools.codegen.DefaultGenerator.generateModels(DefaultGenerator.java:443)
        at org.openapitools.codegen.DefaultGenerator.generate(DefaultGenerator.java:1291)
        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 "var.allowableValues" is null
        at org.openapitools.codegen.DefaultCodegen.getEnumValueForProperty(DefaultCodegen.java:3221)
        at org.openapitools.codegen.DefaultCodegen.lambda$setEnumDiscriminatorDefaultValue$17(DefaultCodegen.java:3193)
        at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:184)
        at java.base/java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:179)
        at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1708)
        at java.base/java.util.stream.ReferencePipeline$Head.forEach(ReferencePipeline.java:762)
        at java.base/java.util.stream.ReferencePipeline$7$1.accept(ReferencePipeline.java:276)
        at java.base/java.util.Spliterators$ArraySpliterator.forEachRemaining(Spliterators.java:1024)
        at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:509)
        at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:499)
        at java.base/java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:151)
        at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:174)
        at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
        at java.base/java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:596)
        at org.openapitools.codegen.DefaultCodegen.setEnumDiscriminatorDefaultValue(DefaultCodegen.java:3193)
        at org.openapitools.codegen.languages.AbstractJavaCodegen.fromModel(AbstractJavaCodegen.java:1842)
        at org.openapitools.codegen.languages.JavaClientCodegen.fromModel(JavaClientCodegen.java:1070)
        at org.openapitools.codegen.DefaultGenerator.processModels(DefaultGenerator.java:1753)
        at org.openapitools.codegen.DefaultGenerator.generateModels(DefaultGenerator.java:513)
        ... 5 more

openapi-generator version

7.16.0 (and also confirmed on the latest master branch).

OpenAPI declaration file content or url

The error occurs when processing the following Node definition (from openapi.yaml, starting at line 3543):

YAML

    Node:
      oneOf:
        - $ref: "#/components/schemas/BooleanOperationNode"
        - $ref: "#/components/schemas/ComponentNode"
        - $ref: "#/components/schemas/ComponentSetNode"
        - $ref: "#/components/schemas/ConnectorNode"
        - $ref: "#/components/schemas/EllipseNode"
        - $ref: "#/components/schemas/EmbedNode"
        - $ref: "#/components/schemas/FrameNode"
        - $ref: "#/components/schemas/GroupNode"
        - $ref: "#/components/schemas/InstanceNode"
        - $ref: "#/components/schemas/LineNode"
        - $ref: "#/components/schemas/LinkUnfurlNode"
        - $ref: "#/components/schemas/RectangleNode"
        - $ref: "#/components/schemas/RegularPolygonNode"
        - $ref: "#/components/schemas/SectionNode"
        - $ref: "#/components/schemas/ShapeWithTextNode"
        - $ref: "#/components/schemas/SliceNode"
        - $ref: "#/components/schemas/StarNode"
        - $ref: "#/components/schemas/StickyNode"
        - $ref: "#/components/schemas/TableNode"
        - $ref: "#/components/schemas/TableCellNode"
        - $ref: "#/components/schemas/TextNode"
        - $ref: "#/components/schemas/TextPathNode"
        - $ref: "#/components/schemas/TransformGroupNode"
        - $ref: "#/components/schemas/VectorNode"
        - $ref: "#/components/schemas/WashiTapeNode"
        - $ref: "#/components/schemas/WidgetNode"
        - $ref: "#/components/schemas/DocumentNode"
        - $ref: "#/components/schemas/CanvasNode"
      discriminator:
        propertyName: type
        mapping:
          BOOLEAN_OPERATION: "#/components/schemas/BooleanOperationNode"
          COMPONENT: "#/components/schemas/ComponentNode"
          COMPONENT_SET: "#/components/schemas/ComponentSetNode"
          CONNECTOR: "#/components/schemas/ConnectorNode"
          ELLIPSE: "#/components/schemas/EllipseNode"
          EMBED: "#/components/schemas/EmbedNode"
          FRAME: "#/components/schemas/FrameNode"
          GROUP: "#/components/schemas/GroupNode"
          INSTANCE: "#/components/schemas/InstanceNode"
          LINE: "#/components/schemas/LineNode"
          LINK_UNFURL: "#/components/schemas/LinkUnfurlNode"
          RECTANGLE: "#/components/schemas/RectangleNode"
          REGULAR_POLYGON: "#/components/schemas/RegularPolygonNode"
          SECTION: "#/components/schemas/SectionNode"
          SHAPE_WITH_TEXT: "#/components/schemas/ShapeWithTextNode"
          SLICE: "#/components/schemas/SliceNode"
          STAR: "#/components/schemas/StarNode"
          STICKY: "#/components/schemas/StickyNode"
          TABLE: "#/components/schemas/TableNode"
          TABLE_CELL: "#/components/schemas/TableCellNode"
          TEXT: "#/components/schemas/TextNode"
          TEXT_PATH: "#/components/schemas/TextPathNode"
          TRANSFORM_GROUP: "#/components/schemas/TransformGroupNode"
          VECTOR: "#/components/schemas/VectorNode"
          WASHI_TAPE: "#/components/schemas/WashiTapeNode"
          WIDGET: "#/components/schemas/WidgetNode"
          DOCUMENT: "#/components/schemas/DocumentNode"
          CANVAS: "#/components/schemas/CanvasNode"

Generation Details

The java generator is being used (likely with default libraries).

Command to reproduce (using CLI Node.js)

openapi-generator-cli generate -i openapi.yaml -g java -o ./types/java

Steps to reproduce

1. Use a valid OpenAPI 3.1 spec (e.g., openapi.yaml) that contains the Node schema provided above.
2. Run the java generator against this spec using either the Node.js CLI or the Java JAR
3. The generation process will crash when attempting to process the Node model.
4. Observe the RuntimeException caused by the NullPointerException in the console output.

Related issues/PRs

• [BUG][JAVA][SPRING] Not able to generate code from spec file with webhooks definition
• [BUG] Presence of path parameter in parent reference triggers NPE while processing examples

[Mattias-Sehlstedt]

As far as I am aware the generator does not support a oneOf-structure where each subSchema has the discriminator type be an enum that only defines a single value (that is a subset of a true larger whole). I.e., having

properties:
  type:
    type: string
    enum:
      - SECTION
    description: The type of this node, represented by the string literal "SECTION"

and

properties:
  type:
    type: string
    enum:
      - FRAME
    description: The type of this node, represented by the string literal "FRAME"

This is an issue since the generator tries to create a parent that contains all types, and if all the children are split, then it is not intuitive to create this enum.

I would suggest trying to have all children define the whole enum (and let the description state which one that is relevant for each type). You could also try to use the 3.1 const and see if that has an impact (the more proper way of expressing a constant value).

If you have no direct control of the specification that you generate a client for (which I assume is the case since it looks to be Figma), then you could investigate normalizing (correcting the specification) with the openapi-generator.

[Radenixlol]

I'm going to try what you mentioned to see if I can make a more accurate change, but it still seems to me that it's an issue that needs to be resolved. This code is generated without problems up to version 7.11.0 of this tool, from 7.12.0 onwards it doesn't work, and it doesn't generate problems when compiling in other languages (I tried it in Kotlin and it worked for example).

[Mattias-Sehlstedt]

Given the background of it being a regression, and the versions that you provide, I would assume that it is likely that it is caused by this change #19614.

If it has worked before, I am also of the opinion that it should be reinstated (since it is a valid way of expressing a oneOf discriminator). So if there is no hurry to get it adjusted on your end, I would hope for a fix within the project instead.

[Radenixlol]

Ok, as long as it's on the list of pending issues to be resolved, I'm fine, especially because they already announced that they will update the version to be generated to JDK17. I'll see if I can find an alternative to its normal operation in 7.16, while I generate code using 7.11.