go-swagger: Client generation fails with `object has no key "UserBase"`

Problem statement

Client generation fails with object has no key "UserBase"

Swagger specification

2.0

Steps to reproduce

1. Create two files first.yml

swagger: '2.0'

info:
  version: '2.0'
  title: test
  description: test
  license:
    name: N/A

basePath: /v2

schemes:
  - http
  - https

consumes:
  - application/json
produces:
  - application/json

paths:
  /user:
    get:
      operationId: getUser
      description: test
      responses:
        200:
          description: succes
          schema:
            $ref: 'second.yml#/definitions/User'

/second.yml

swagger: '2.0'

info:
  version: '2.0'
  title: test
  description: test
  license:
    name: N/A

basePath: /v2

schemes:
  - http
  - https

consumes:
  - application/json
produces:
  - application/json

definitions:
  UserBase:
    type: object
    properties:
      id:
        type: integer
        format: uint64

  User:
    allOf:
    - $ref: '#/definitions/UserBase'
    - properties:
        createdAt:
          type: string
          format: date-time
        updatedAt:
          type: string
          format: date-time

1. run swagger generate client -f /Users/andrew/Workspace/go/src/github.com/go-swagger/example/first.yml -t /Users/andrew/Workspace/go/src/github.com/go-swagger/example/gen --skip-validation
2. swagger returns object has no key "UserBase"

Environment

swagger version: latest from the master 220a68f31437616b53c032a5f82384450f82cf4e go version: go version go1.8.3 darwin/amd64 OS: MacOS Sierra 10.12.5