[JAVA] Incorrect java code gen when enum has only one element

swagger-codegen-maven-plugin 2.2.2

    "action" : {
      "type" : "string",
      "enum" : [ "MOVE_TO_GROUP" ]
    },

Generates this

     public enum ActionEnum {
          GROUP("MOVE_TO_GROUP"),
           ...

Should be

     public enum ActionEnum {
           MOVE_TO_GROUP("MOVE_TO_GROUP"),

Work around - add dummy second element

    "action" : {
      "type" : "string",
      "enum" : [ "MOVE_TO_GROUP", "UNSUPPORTED" ]
    },

enum with one element makes no sense, but i think it should be fixed

Start with the swagger-codegen-maven-plugin and reproduce generation using the provided schema with a single-value enum. Trace the Java enum generation path and verify that the generated constant uses MOVE_TO_GROUP rather than GROUP; the workaround and expected output in the issue define done.