[BUG][JAVA] Error when generating nullable byte array

[Polly-Schulze]

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

Description

When there is a nullable byte array in the json file:

          "SomeByteArray": {
            "type": "object",
            "description": "something",
            "additionalProperties": false,
            "properties": {
              "someField": {
                "type": "string",
                "description": "byte array.",
                "format": "byte",
                "nullable": true
              }
            }
          }

Then the file generated looks like this:

@ApiModel(description = "something")
@JsonPropertyOrder({
  SomeByteArray.JSON_PROPERTY_SOME_FIELD
})
@javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", date = "2021-07-21T10:10:33.395362+02:00[Europe/Berlin]")
public class SomeByteArray {
  public static final String JSON_PROPERTY_SOME_FIELD = "someField";
  private JsonNullable<byte[]> someField = JsonNullable.<byte[]>undefined();

// GETTER AND SETTER

  /**
   * Return true if this SomeByteArray object is equal to o.
   */
  @Override
  public boolean equals(Object o) {
    if (this == o) {
      return true;
    }
    if (o == null || getClass() != o.getClass()) {
      return false;
    }
    SomeByteArray someByteArray = (SomeByteArray) o;
    return Arrays.equals(this.someField, someByteArray.someField);
  }

// HASH CODE etc.
}

This results in an compiler error, since Arrays.equals(this.someField, someByteArray.someField); compares Arrays, but someField is a JsonNullable of an Array.
In an earlier version the line was generated to: Objects.equals(this.someField, someByteArray.someField);, which does not result in an error.

openapi-generator version

In this version:
java -jar ~/Downloads/openapi-generator-cli-4.3.1.jar generate -g spring --additional-properties=library=spring-mvc -o minimalExample -i src/main/resources/minimalExample.json
the error does not occur as there are still Objects compared, not Arrays.

In the newest version of different libraries the error occurs:
java -jar ~/Downloads/openapi-generator-cli-5.2.0.jar generate -g spring --additional-properties=library=spring-mvc -o minimalExample-2 -i src/main/resources/minimalExample.json

java -jar ~/Downloads/openapi-generator-cli-5.2.0.jar generate -g java --additional-properties=library=webclient -o minimalExample-3 -i src/main/resources/minimalExample.json

java -jar ~/Downloads/openapi-generator-cli-5.2.0.jar generate -g java --additional-properties=library=jersex2 -o minimalExample-4 -i src/main/resources/minimalExample.json

Java version:

 ~ java -version
openjdk version "16.0.1" 2021-04-20
OpenJDK Runtime Environment AdoptOpenJDK-16.0.1+9 (build 16.0.1+9)
OpenJDK 64-Bit Server VM AdoptOpenJDK-16.0.1+9 (build 16.0.1+9, mixed mode, sharing)

OpenAPI declaration file content or url

{
  "x-generator": "NSwag v13.11.3.0 (NJsonSchema v10.4.4.0 (Newtonsoft.Json v13.0.0.0))",
  "openapi": "3.0.0",
  "info": {
    "title": "Minimal Example ",
    "description": "byte Array error in equal method",
    "version": "v1"
  },
  "paths": {
    "/some/path/": {
      "get": {
        "summary": "",
        "description": "",
        "operationId": "",
        "parameters": [],
        "responses": {
          "200": {
            "description": "",
            "content": {
              "application/json": {
                "schema": {
                  "type": "array",
                  "items": {
                    "$ref": "#/components/schemas/SomeByteArray"
                  }
                }
              }
            }
          }
        }
      }
    }
  },
      "components": {
        "schemas": {
          "SomeByteArray": {
            "type": "object",
            "description": "something",
            "additionalProperties": false,
            "properties": {
              "someField": {
                "type": "string",
                "description": "byte array.",
                "format": "byte",
                "nullable": true
              }
            }
          }
        }
      }
}

Steps to reproduce

1. Save the code above as json
2. Execute one of the above (see part about version)
3. Check the file SomeByteArray.java

[wing328]

Fixed by #10012 contributed by @borsch . Thanks for the fix.