[BUG] [JAVA] [webclient] addXYZ Builder Method in Pojo produces NullPointerException for nullable array properties

[kzander91]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• 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?

Description

For nullable arrays, the POJO generated by 6.3.0 no longer initializes the property with an empty list when using the addXYZ(T item) builder method to add an item to the property. This produces a NullPointerException. With 6.2.1, if the JsonNullable didn't contain a value, it was initialized with a new ArrayList.

Generated builder method with 6.2.1:

public class TestObject {
  // other stuff

  private JsonNullable<List<String>> nullableArrayProp = JsonNullable.<List<String>>undefined();

  // other stuff

  public TestObject addNullableArrayPropItem(String nullableArrayPropItem) {
    if (this.nullableArrayProp == null || !this.nullableArrayProp.isPresent()) {
      this.nullableArrayProp = JsonNullable.<List<String>>of(new ArrayList<>()); // <-- initialized with empty list
    }
    try {
      this.nullableArrayProp.get().add(nullableArrayPropItem); // <-- no NPE here
    } catch (java.util.NoSuchElementException e) {
      // this can never happen, as we make sure above that the value is present
    }
    return this;
  }

  // other stuff
}

Generated builder method with 6.3.0:

public class TestObject {
  // other stuff

  private JsonNullable<List<String>> nullableArrayProp = JsonNullable.<List<String>>undefined();

  // other stuff

  public TestObject addNullableArrayPropItem(String nullableArrayPropItem) {
    if (this.nullableArrayProp == null || !this.nullableArrayProp.isPresent()) {
      this.nullableArrayProp = JsonNullable.<List<String>>of(null); // <-- initialized with null
    }
    try {
      this.nullableArrayProp.get().add(nullableArrayPropItem); // NPE here
    } catch (java.util.NoSuchElementException e) {
      // this can never happen, as we make sure above that the value is present
    }
    return this;
  }

  // other stuff
}

openapi-generator version

6.3.0 (no errors with 6.2.1)

OpenAPI declaration file content or url

openapi: 3.0.3
info:
    title: Title
    version: "1"
paths:
  /test:
    get:
      responses:
        200:
          description: Success
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/TestObject'
components:
  schemas:
    TestObject:
      type: object
      properties:
        myNullableArrayProp:
          type: array
          nullable: true
          items:
            type: string

Generation Details

java -jar openapi-generator-cli-6.3.0.jar generate -g java --library webclient -i spec.yaml -o out

Steps to reproduce

1. Model with attribute of type array and nullable: true.
2. Generate with generator java and library webclient.
3. TestObject#addMyNullableArrayPropItem initializes property value with null, causing a NullPointerException in the next statement.

Related issues/PRs

#14130

Suggest a fix

Check if the property's type is array, initialize it with an empty ArrayList, as before.

[wing328]

can you set the option containerDefaultToNull to true to see if that works?

[kzander91]

Both
java -jar openapi-generator-cli-6.3.0.jar generate -g java --library webclient --additional-properties=containerDefaultToNull=false -i spec.yaml -o out
and
java -jar openapi-generator-cli-6.3.0.jar generate -g java --library webclient --additional-properties=containerDefaultToNull=true -i spec.yaml -o out
produce identical output and don't fix this.

[wing328]

what about setting nullable to false instead?

[kzander91]

With nullable: false and containerDefaultToNull=false, the NPE is fixed:

  public TestObject addMyNullableArrayPropItem(String myNullableArrayPropItem) {
    if (this.myNullableArrayProp == null) {
      this.myNullableArrayProp = new ArrayList<>();
    }
    this.myNullableArrayProp.add(myNullableArrayPropItem);
    return this;
  }

With nullable: false and containerDefaultToNull=true, it is not:

  public TestObject addMyNullableArrayPropItem(String myNullableArrayPropItem) {
    if (this.myNullableArrayProp == null) {
      this.myNullableArrayProp = null;
    }
    this.myNullableArrayProp.add(myNullableArrayPropItem);
    return this;
  }

For completeness, here's the other two permutations:
nullable: true, containerDefaultToNull=false:

  public TestObject addMyNullableArrayPropItem(String myNullableArrayPropItem) {
    if (this.myNullableArrayProp == null || !this.myNullableArrayProp.isPresent()) {
      this.myNullableArrayProp = JsonNullable.<List<String>>of(null);
    }
    try {
      this.myNullableArrayProp.get().add(myNullableArrayPropItem);
    } catch (java.util.NoSuchElementException e) {
      // this can never happen, as we make sure above that the value is present
    }
    return this;
  }

nullable: true, containerDefaultToNull=true (identical):

  public TestObject addMyNullableArrayPropItem(String myNullableArrayPropItem) {
    if (this.myNullableArrayProp == null || !this.myNullableArrayProp.isPresent()) {
      this.myNullableArrayProp = JsonNullable.<List<String>>of(null);
    }
    try {
      this.myNullableArrayProp.get().add(myNullableArrayPropItem);
    } catch (java.util.NoSuchElementException e) {
      // this can never happen, as we make sure above that the value is present
    }
    return this;
  }

[wing328]

thanks for the info. i'll try to come up with a PR to address it this or next week.

[wing328]

We want to use nullable to determine whether we should use null (nullable: true) or empty array/maps/set (nullable: false).

[tofi86]

Also happens for the JavaSpring generator.

[MelleD]

@wing328 do you know why this changes from a empty collection to a null value? Make this sense into a JsonNullable?

For us the empty collection (List or Set) was fine and works.

[wing328]

Hi all,

I've file a fix: #14703. Please test it when you've time to confirm it addresses the issues in your use cases.

Thank you.

[wing328]

PR merged. Please give it a try with the SNAPSHOT JAR https://oss.sonatype.org/content/repositories/snapshots/org/openapitools/openapi-generator-cli/6.3.0-SNAPSHOT/openapi-generator-cli-6.3.0-20230201.075320-98.jar https://oss.sonatype.org/content/repositories/snapshots/org/openapitools/openapi-generator-cli/6.4.0-SNAPSHOT/openapi-generator-cli-6.4.0-20230216.072505-21.jar and let me know if you still encounter the issue.

[kzander91]

@wing328: The SNAPSHOT jar produces identical output and thus doesn't fix the issue.
I tried all four scenarios from my previous comment.

[wing328]

Can you try https://oss.sonatype.org/content/repositories/snapshots/org/openapitools/openapi-generator-cli/6.4.0-SNAPSHOT/openapi-generator-cli-6.4.0-20230216.072505-21.jar instead ? (6.4.0-SNAPSHOT JAR)

Sorry that the one I provided earlier was for v6.3.0 (which was released already).

[kzander91]

The new snapshot fixed the issue for the example spec. Give me a bit more time to verify that with my actual application.

[wing328]

Please run more tests 🙏

[kzander91]

@wing328: I successfully tested the snapshot with my actual application, so this fix works for me, thanks for the fix.

[VinceGall]

Same issue