[nodejs-server] silently exits for swagger-hub example

Description

I ran both the brew 3.0.4 version of the tool and compiled 3.0.5 and had the same issue.

java -jar modules/swagger-codegen-cli/target/swagger-codegen-cli.jar generate -i ~/Documents/swagger/test.yaml -o ~/Documents/swagger/ -l nodejs-server
cd ~/Documents/swagger/test.yaml
npm run start

output:

> simple-inventory-api@1.0.0 prestart /Users/ben/Documents/swagger
> npm install

npm notice created a lockfile as package-lock.json. You should commit this file.
added 130 packages from 79 contributors and audited 414 packages in 6.917s
found 0 vulnerabilities


> simple-inventory-api@1.0.0 start /Users/ben/Documents/swagger
> node index.js
# silent exit

I expect the server to stay open so I can send it requests.

Swagger-codegen version

3.0.4 and 3.0.5

Swagger declaration file content or url

openapi: 3.0.0
# Added by API Auto Mocking Plugin
servers:
  - description: SwaggerHub API Auto Mocking
    url: https://virtserver.swaggerhub.com/trellis/test/1.0.0
info:
  description: This is a simple API
  version: "1.0.0"
  title: Simple Inventory API
  contact:
    email: you@your-company.com
  license:
    name: Apache 2.0
    url: 'http://www.apache.org/licenses/LICENSE-2.0.html'
tags:
  - name: admins
    description: Secured Admin-only calls
  - name: developers
    description: Operations available to regular developers
paths:
  /inventory:
    get:
      tags:
        - developers
      summary: searches inventory
      operationId: searchInventory
      description: |
        By passing in the appropriate options, you can search for
        available inventory in the system
      parameters:
        - in: query
          name: searchString
          description: pass an optional search string for looking up inventory
          required: false
          schema:
            type: string
        - in: query
          name: skip
          description: number of records to skip for pagination
          schema:
            type: integer
            format: int32
            minimum: 0
        - in: query
          name: limit
          description: maximum number of records to return
          schema:
            type: integer
            format: int32
            minimum: 0
            maximum: 50
      responses:
        '200':
          description: search results matching criteria
          content:
            application/json:
              schema:
                type: array
                items:
                  $ref: '#/components/schemas/InventoryItem'
        '400':
          description: bad input parameter
    post:
      tags:
        - admins
      summary: adds an inventory item
      operationId: addInventory
      description: Adds an item to the system
      responses:
        '201':
          description: item created
        '400':
          description: 'invalid input, object invalid'
        '409':
          description: an existing item already exists
      requestBody:
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/InventoryItem'
        description: Inventory item to add
components:
  schemas:
    InventoryItem:
      type: object
      required:
        - id
        - name
        - manufacturer
        - releaseDate
      properties:
        id:
          type: string
          format: uuid
          example: d290f1ee-6c54-4b01-90e6-d701748f0851
        name:
          type: string
          example: Widget Adapter
        releaseDate:
          type: string
          format: date-time
          example: '2016-08-29T09:12:33.001Z'
        manufacturer:
          $ref: '#/components/schemas/Manufacturer'
    Manufacturer:
      required:
        - name
      properties:
        name:
          type: string
          example: ACME Corporation
        homePage:
          type: string
          format: url
          example: 'https://www.acme-corp.com'
        phone:
          type: string
          example: 408-867-5309
      type: object

Command line used for generation

java -jar modules/swagger-codegen-cli/target/swagger-codegen-cli.jar generate -i ~/Documents/swagger/test.yaml -o ~/Documents/swagger/ -l nodejs-server

Steps to reproduce

1. generate documentation
2. npm start
3. server exits unexpectedly

Related issues/PRs

Suggest a fix/enhancement

Reproduce the generation command and inspect the generated index.js and npm start script, beginning with the process entry point that exits immediately. Compare the generated nodejs-server output with the expected long-running server behavior; done means npm start keeps the process open and the generated server can accept requests.