openapi-generator: [BUG] [Java] Nullable field failing when explicitly set to "null"

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Description

In our OpenAPI spec, we have a model with a nullable field called “prev_page_url”. If we test the generated code (with generator v6.0.0) omitting the parameter, it works correctly.

If instead we test setting the field explicitly to null we obtain the following error:

Expected the field `prev_page_url` to be a primitive type in the JSON string but got `null`

openapi-generator version

v6.0.0

OpenAPI declaration file content or URL

The parameter is defined here, and the main spec can be found here

title: Pagination
type: object
description: ''
properties:
  current_page:
    type: integer
    description: Current page number.
    nullable: true
  first_page_url:
    type: string
    format: uri
    description: First page url.
    nullable: true
  from:
    type: integer
    nullable: true
    description: First result of the page.
  last_page:
    type: integer
    description: Last page number.
    nullable: true
  last_page_url:
    type: string
    format: uri
    description: Last page url.
    nullable: true
  next_page_url:
    type: string
    format: uri
    nullable: true
    description: Next page url
  path:
    type: string
    format: uri
    description: Request path.
    nullable: true
  per_page:
    type: integer
    description: Number of result per page.
    nullable: true
  prev_page_url:
    type: string
    format: uri
    nullable: true
    description: Previous page url.
  to:
    type: integer
    nullable: true
    description: Last result of the page.
  total:
    type: integer
    description: Total number of results
    nullable: true

Generation Details

Our github action can be found here openapi-generator-cli generate -i ./openapi.yaml -g java -o ./generated/java/

Steps to reproduce

obtain a JSON response with the parameter set as follows:

{
  "prev_page_url":null
}

Related issues/PRs

I couldn’t find any…

Suggest a fix

In this case, Gson doesn’t set the param to null, but to an instance of JsonNull class. To check it should be able to change the pojo.mustache template in this way:

if (({{^isRequired}}jsonObj.get("{{{baseName}}}") != null && {{^isRequired}}jsonObj.get("{{{baseName}}}").isJsonNull()) && {{/isRequired}}!jsonObj.get("{{{baseName}}}").isJsonPrimitive()) {

If you want, I can try to prepare a PR for this issue.

About this issue

Original URL
State: open
Created 2 years ago
Reactions: 6
Comments: 23 (8 by maintainers)

Most upvoted comments

Hi, I prepared a PR for this https://github.com/OpenAPITools/openapi-generator/pull/12630 I’ll try to launch the sample generation as soon as possible, to make it acceptable for the team.

valmoz on Jun 17, 2022

Im using v6.2.1 and am generating a Java client with:

openapi-generator generate -i swagger.yaml -g java -o ./generated/ledger \
  --group-id com.clever \
  --api-package com.clever.sdk.ledgerdataservice.api \
  --artifact-id ledger-data-service-java-client \
  --model-package com.clever.sdk.ledgerdataservice.models \
  --additional-properties=dateLibrary=java8,library=okhttp-gson

When any property is null, even if including nullable: true in the definition, eg

Expected the field currencyCodeto be a primitive type in the JSON string but gotnull``

Is this fixed by the PR above? It doesnt seem to be for Java

Zander1983 on Dec 7, 2022

I’m also seeing this issue with required: true in combination with nullable: true in Version 6.6.0. Whenever the value is “null”, the validation is throwing an Exception for trying to cast gson.JsonNull to gson.JsonObject.

FloCoop on Jun 5, 2023

I’m also seeing this issue with a required, nullable, readOnly object string property. Particularly the issue seems to be when mixing both nullable and required.

samypr100 on May 9, 2023

I’m on the latest 6.4.0 and still seems to be an issue for arrays when explicitly set to null in the JSON response. The issue in the mustache seems to be this part, perhaps it should also do a check for isJsonNull()?

      // ensure the optional json data is an array if present
      if (jsonObj.get("{{{baseName}}}") != null && !jsonObj.get("{{{baseName}}}").isJsonArray()) {
        throw new IllegalArgumentException(String.format("Expected the field `{{{baseName}}}` to be an array in the JSON string but got `%s`", jsonObj.get("{{{baseName}}}").toString()));
      }

jaavaguy on Mar 6, 2023

This fix works for me (using v6.3.0), so should probably be closed

nikosmoum on Feb 22, 2023

@aaron-613 I just modified one mustache file… and then launched the generator to update the example files

valmoz on Sep 8, 2022

Hi @aaron-613 my PR was merged, but I think it will be released in the next milestone. https://github.com/OpenAPITools/openapi-generator/pull/12630

valmoz on Sep 8, 2022

I’m affected by this issue as well and I am interested in fixing it. I will submit a PR for it if @valmoz is not already working on it.

petitcl on Jun 16, 2022