[Java] Codegen for definition with no properties leads to invalid Java

Description

The swagger file is generated from an external model. For whatever reason (not too important), a definition has no properties. The Java class for this definition is not generated, but references to that class are generated in the model code, leading to compilation errors.

Swagger-codegen version

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

NOTE:
Also replicates with 2.2.1

Swagger declaration file content or url

Below see an edited version of the swagger file, removed all paths and not required definitions

{
  "swagger": "2.0",
  "info": {
    "version": "v2",
    "title": "StayinFront.WebAPI V2"
  },
  "host": "localhost",
  "basePath": "/revapi",
  "schemes": [
    "http"
  ],
  "paths": {},
  "definitions": {
    "CHT_ChannelWF_PutData": {
      "description": "CHT_ChannelWF_PutData",
      "properties": {}
    },
    "CHT_Channel_PutData": {
      "description": "CHT_Channel_PutData",
      "properties": {
        "WF": {
          "$ref": "#/definitions/CHT_ChannelWF_PutData"
        }
      }
    }
  }
}

This generates invalid Java:

...

package io.swagger.client.model;

import java.util.Objects;
import com.google.gson.annotations.SerializedName;
import io.swagger.annotations.ApiModel;
import io.swagger.annotations.ApiModelProperty;
import io.swagger.client.model.CHTChannelWFPutData;


/**
 * CHT_Channel_PutData
 */
@ApiModel(description = "CHT_Channel_PutData")
@javax.annotation.Generated(value = "class io.swagger.codegen.languages.JavaClientCodegen", date = "2017-02-16T09:36:18.569+13:00")
public class CHTChannelPutData   {
  @SerializedName("WF")
  private CHTChannelWFPutData WF = null;

  public CHTChannelPutData WF(CHTChannelWFPutData WF) {
    this.WF = WF;
    return this;
  }

   /**
   * Get WF
   * @return WF
  **/
  @ApiModelProperty(example = "null", value = "")
  public CHTChannelWFPutData getWF() {
    return WF;
  }

  public void setWF(CHTChannelWFPutData WF) {
    this.WF = WF;
  }

...
}

The actual class CHTChannelWFPutData is not generated so the above is nonsense. I would expect that CHTChannelWFPutData was generated.

Command line used for generation

java -jar swagger-codegen\snapshot\swagger-codegen-cli-2.2.1.jar generate -i swagger-file.json -l java -o output-dir

Steps to reproduce

1. generate Java source using the above command line
2. attempt to compile

Related issues

I couldn't find any related

Start by running the supplied Java code-generation command with the reduced Swagger JSON and inspect the Java model-generation entry point for definitions with empty properties. Add coverage for the empty definition and verify that the referenced Java class is generated and the resulting model sources compile.