[BUG] Description openapi-generator can't build AnyOf object that contains an empty value using Java (openapi: 3.1.0)

[itsRyanTreanor]

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

Description

openapi-generator version

7.14.0

When I am trying the generate the below openAPI definition, it does not correctly build the anyOf object. This openAPI definition is from a third party company that we are trying to integrate with.

      "CustomMetric": {
        "properties": {
          "name": {
            "type": "string",
            "title": "Name"
          },
          "description": {
            "type": "string",
            "title": "Description"
          },
          "value": {
            "anyOf": [
              {

              },
              {
                "type": "null"
              }
            ],
            "title": "Value"
          }
        },
        "type": "object",
        "required": [
          "name",
          "description",
          "value"
        ],
        "title": "CustomMetric"
      }

Generation Details

mvn clean generate-sources
mvn clean test

            <configuration>
                <groupId>${project.groupId}</groupId>
                <artifactId>${project.artifactId}</artifactId>
                <artifactVersion>${project.version}</artifactVersion>
                <generatorName>java</generatorName>
                <library>resttemplate</library>
                <generateApis>false</generateApis>
                <generateSupportingFiles>false</generateSupportingFiles>
                <configOptions>
                    <java8>true</java8>
                    <dateLibrary>java8</dateLibrary>
                    <licenseName>Apache 2.0</licenseName>
                    <licenseUrl>https://www.apache.org/licenses/LICENSE-2.0</licenseUrl>
                    <openApiNullable>false</openApiNullable>
                    <useJakartaEe>false</useJakartaEe>
                    <useOneOfInterfaces>false</useOneOfInterfaces>
                    <legacyDiscriminatorBehavior>true</legacyDiscriminatorBehavior>
                </configOptions>
            </configuration>

Steps to reproduce

Related issues/PRs

Suggest a fix

[wing328]

can you try the latest stable version, which may offer better normalization of anyOf schema for this edge case?

[itsRyanTreanor]

@wing328 I have updated to 7.19.0 and I see the same issue:

"openapi": "3.1.0"

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.8.1:compile (default-compile) on project yyyyy-generated: Compilation failure: Compilation failure:
[ERROR] /C:/Users/USER/Development/Repos/yyyyy-generated/target/generated-sources/openapi/src/main/java/com/xxxx/integration/yyyyy/generated/model/CustomMetric.java:[23,60] cannot find symbol
[ERROR]   symbol:   class AnyOf
[ERROR]   location: package com.xxxx.integration.yyyyy.generated.model
[ERROR] /C:/Users/USER/Development/Repos/yyyyy-generated/target/generated-sources/openapi/src/main/java/com/xxxx/integration/yyyyy/generated/model/CustomMetric.java:[47,11] cannot find symbol
[ERROR]   symbol:   class AnyOf
[ERROR]   location: class com.xxxx.integration.yyyyy.generated.model.CustomMetric
[ERROR] /C:/Users/USER/Development/Repos/yyyyy-generated/target/generated-sources/openapi/src/main/java/com/xxxx/integration/yyyyy/generated/model/CustomMetric.java:[102,56] cannot find symbol
[ERROR]   symbol:   class AnyOf
[ERROR]   location: class com.xxxx.integration.yyyyy.generated.model.CustomMetric
[ERROR] /C:/Users/USER/Development/Repos/yyyyy-generated/target/generated-sources/openapi/src/main/java/com/xxxx/integration/yyyyy/generated/model/CustomMetric.java:[116,10] cannot find symbol
[ERROR]   symbol:   class AnyOf
[ERROR]   location: class com.xxxx.integration.yyyyy.generated.model.CustomMetric
[ERROR] /C:/Users/USER/Development/Repos/yyyyy-generated/target/generated-sources/openapi/src/main/java/com/xxxx/integration/yyyyy/generated/model/CustomMetric.java:[123,51] cannot find symbol
[ERROR]   symbol:   class AnyOf
[ERROR]   location: class com.xxxx.integration.yyyyy.generated.model.CustomMetric
[ERROR] -> [Help 1]
[ERROR]

@javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", date = "2026-01-27T11:16:17.922261800Z[Europe/London]", comments = "Generator version: 7.19.0")
public class CustomMetric {
  public static final String JSON_PROPERTY_NAME = "name";
  @javax.annotation.Nonnull
  private String name;

  public static final String JSON_PROPERTY_DESCRIPTION = "description";
  @javax.annotation.Nonnull
  private String description;

  public static final String JSON_PROPERTY_VALUE = "value";
  @javax.annotation.Nullable
  private AnyOf value;

      "CustomMetric": {
        "properties": {
          "name": {
            "type": "string",
            "title": "Name"
          },
          "description": {
            "type": "string",
            "title": "Description"
          },
          "value": {
            "anyOf": [
              {

              },
              {
                "type": "null"
              }
            ],
            "title": "Value"
          }
        },
        "type": "object",
        "required": [
          "name",
          "description",
          "value"
        ],
        "title": "CustomMetric"
      }

[Mattias-Sehlstedt]

What type of object/class generation are we expecting? Just a standard Object? To me

"value": {
  "anyOf": [
    {

    },
    {
      "type": "null"
    }
  ],
  "title": "Value"
}

looks like an odd/superfluous way of saying

"value": {
  "schema": {},
  "title": "Value"
}

But I am not sure that the latter currently works either.