[JAVA] codegen with negative integer enum values compile error

Description

I have an enum in my swagger doc:

  enums/TimeValidationZone:
    description: TimeValidationZone
    type: object
    properties:
      description:
        description: description
        type: string
      data:
        enum:
          - '-720'
          - '-660'
          - '-600'
          - '-540'
          - '-480'
          - '-420'
          - '-360'
          - '-300'
          - '-240'
          - '-210'
          - '-180'
          - '-120'
          - '-60'
          - '0'
          - '60'
          - '120'
          - '180'
          - '210'
          - '240'
          - '270'
          - '300'
          - '330'
          - '345'
          - '360'
          - '390'
          - '420'
          - '480'
          - '540'
          - '570'
          - '600'
          - '660'
          - '720'
          - '780'
        type: string

The salient point being that there is negative values with the same absolute value e.g. -60 and 60.

This generates invalid Java code:

@ApiModel(description = "TimeValidationZone")
@javax.annotation.Generated(value = "class io.swagger.codegen.languages.JavaClientCodegen", date = "2017-02-13T15:17:56.985+13:00")
public class EnumsTimeValidationZone {
  @SerializedName("description")
  private String description = null;

  /**
   * Gets or Sets data
   */
  public enum DataEnum {

    ...

    @SerializedName("-60")
    _60("-60"),
    
    @SerializedName("0")
    _0("0"),
    
    @SerializedName("60")
    _60("60"),

    ...

Swagger-codegen version

λ java -jar swagger-codegen\modules\swagger-codegen-cli\target\swagger-codegen-cli.jar version
2.2.2-SNAPSHOT

Swagger declaration file content or url

See above for relevant portion.

Command line used for generation

java -jar swagger-codegen\modules\swagger-codegen-cli\target\swagger-codegen-cli.jar generate -i http://localhost/revapi/swagger/docs/v2 -l java -o .\swagger-java-client\

Steps to reproduce

Create swagger file with enum type as declared above, run codegen.