[JAVA] Bug generating models with enum discriminator

Description

The model for an object with an enum discriminator generates a constructor that causes a compilation error.

The following is an example generated model with some irrelevant code removed.

package com.alianza.client.model;

// imports

public class RingFailoverAction {
  /**
   * Gets or Sets type
   */
  @JsonAdapter(TypeEnum.Adapter.class)
  public enum TypeEnum {
    // values

    private String value;

    TypeEnum(String value) {
      this.value = value;
    }

    public String getValue() {
      return value;
    }

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

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

    public static class Adapter extends TypeAdapter<TypeEnum> {
      @Override
      public void write(final JsonWriter jsonWriter, final TypeEnum enumeration) throws IOException {
        jsonWriter.value(enumeration.getValue());
      }

      @Override
      public TypeEnum read(final JsonReader jsonReader) throws IOException {
        String value = jsonReader.nextString();
        return TypeEnum.fromValue(String.valueOf(value));
      }
    }
  }

  @SerializedName("@type")
  private TypeEnum type = null;

  public RingFailoverAction() {
    this.type = this.getClass().getSimpleName();
  }
  public RingFailoverAction type(TypeEnum type) {
    this.type = type;
    return this;
  }

   /**
   * Get type
   * @return type
  **/
  @ApiModelProperty(required = true, value = "")
  public TypeEnum getType() {
    return type;
  }

  public void setType(TypeEnum type) {
    this.type = type;
  }

  // equals

  // hashCode

  // toString

  // toIndentedString
}

The statement causing the error is this.type = this.getClass().getSimpleName(), which is attempting to assign a String to a TypeEnum.

Swagger-codegen version

2.4.15 (not a regression)

Swagger declaration file content or url

Full file: https://api.alianza.com/v2/apidocs/swagger.json

Relevant example section

"RingFailoverAction" : {
  "type" : "object",
  "required" : [ "@type" ],
  "discriminator" : "@type",
  "properties" : {
    "@type" : {
      "type" : "string",
      "enum" : [ "VoicemailRingFailoverAction", "BusyRingFailoverAction", "ForwardRingFailoverAction" ]
    }
  }
}

Command line used for generation

java -jar swagger-codegen-cli-2.4.15.jar generate -i https://api.alianza.com/v2/apidocs/swagger.json --api-package com.alianza.client.api --model-package com.alianza.client.model --invoker-package com.alianza.client.invoker --group-id com.alianza -l java -o ./generated_java_client --additional-properties dateLibrary=java8

Steps to reproduce

1. Run the command line
2. Attempt to compile

Related issues/PRs

https://github.com/swagger-api/swagger-codegen/issues/10196#issuecomment-659673863

Suggest a fix/enhancement

Wrapping this.getClass().getSimpleName() with the enum's valueOf() fixes the compilation error, but I don't know if this is the proper fix because I don't know what the use of that constructor even is.

Start by running the reported swagger-codegen-cli command against the linked Swagger declaration and inspect the Java output for RingFailoverAction. Trace the constructor generation for the enum discriminator, then verify the generated client compiles without assigning a String to TypeEnum.