[Java, Jaxrs Spec] Ommitted type in swagger enum generates corrupted Java Enum

Description

When you leave out the type in a enum declaration in a swagger file (which apparently is valid), the generated enum class does not compile because codegen inserts empty string as the enum's type.

Swagger-codegen version

2.4.0 snapshot

Swagger declaration file content or url

  BackendType:
    #type: string
    enum:
      - ILON
      - HUE

leads to:

public enum BackendType {
  
  ILON("ILON"),
  
  HUE("HUE");

  private  value; <------------------------------------

  BackendType( value) { <----------------------------
    this.value = value;
  }

  @Override
  @JsonValue
  public String toString() {
    return String.valueOf(value);
  }

  @JsonCreator
  public static BackendType fromValue(String text) {
    for (BackendType b : BackendType.values()) {
      if (String.valueOf(b.value).equals(text)) {
        return b;
      }
    }
    return null;
  }
}

Command line used for generation

invoked via gradle, language is jax-rs spec
used options:

{
  "interfaceOnly": true,
  "dateLibrary":"java8",
  "invokerPackage": "ch.package.impl",
  "apiPackage" : "ch.package.webapi",
  "modelPackage" : "ch.package.webapi.model",
  "java8" : "true",
  "title" : "App server",
  "returnResponse": true
}

add above definition to a yaml file and generate jax-rs spec server code.

Related issues/PRs

to some degree: #8275

Suggest a fix/enhancement

One of those:

• don't generate a value attribute in the enum (and also ommit constructors) if there is no type specified
• Use string as default if no type specified

Start with the Gradle JAX-RS spec generation entry point and reproduce the issue using the provided Swagger YAML enum without a type. Inspect the generated Java enum and ensure the output compiles with a valid enum value type or without the unnecessary value field and constructor.