[JavaScript] Missing `ModelObject` in JS

Description

When using a oneof with openapi: "3.0.0" the code generates an import inside the models folder for ./ModelObject. models/ModelObject.js is never generated.

Swagger-codegen version

3.0.18

Swagger declaration file content or url

    MyObject:
      title: MyObjectTitle
      type: object
      properties:
        messageType:
          type: string
        message:
          oneOf:
            - $ref: '#/components/schemas/MessageA'
            - $ref: '#/components/schemas/MessageB'
      required:
        - messageType

Command line used for generation

On OSX (installed via brew):

swagger-codegen generate --lang javascript --input my-spec.yml -o ./

Steps to reproduce

Create above model in a yaml file, run generation command, attempt to build project.

Related issues/PRs

N/A

Suggest a fix/enhancement

If we know what the outputted code should be I can shim this into our library to unblock us.

Start with the supplied OpenAPI 3.0.0 YAML and run the shown JavaScript generation command. Inspect the generated models directory and the import of ./ModelObject; done means the generated project builds without a missing ModelObject.js file.