[BUG] [ASPNETCORE] - Invalid model namespace added if no models exist

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
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Description

Generate an OpenAPI declaration file, which contains no models for ASPNETCORE. In the generated controllers an invalid namespace to Models is added, which does not exist.

openapi-generator version

Version: 6.0.1

OpenAPI declaration file content or url

device_registration_api.yaml:

openapi: 3.0.1
info:
  title: Device Registration API
  description: API of the device registration server where phones get their configuration and firmware.
  version: 1.0.0
  contact:
    name: WD
servers:
  - url: 'http://localhost:3000'
tags:
  - name: API
    description: ''
paths:
  '/CTL{MAC}.tlv':
    get:
      tags:
        - API
      summary: Get CTL file of the given MAC address
      description: 'This file is not necessarily required by the phone for the registration process. To keep the file system organized, CTL files should be looked up in a subfolder `ctl` or may be retrieved from a database.'
      operationId: getCTLByMACAddress
      parameters:
        - name: MAC
          in: path
          description: The MAC address of the phone requesting the CTL file
          required: true
          schema:
            type: string
      responses:
        '200':
          description: Requested file is found and is returned to the phone
        '404':
          description: Not Found
    parameters:
      - schema:
          type: string
        name: MAC
        in: path
        required: true
        description: The MAC address of the requesting device

Generation Details

openApiGeneratorConfig.json:

{
  "packageName": "DeviceRegistrationApi",
  "packageTitle": "DeviceRegistrationApi",
  "packageCopyright": "WD2023",
  "packageVersion": "1.0",
  "aspnetCoreVersion": "6.0",
  "buildTarget": "library",
  "isLibrary": "true",
  "operationIsAsync": "true",
  "operationResultTask": "true",
  "nullableReferenceTypes": "true",
  "operationModifier": "abstract",
  "swashbuckleVersion": "6.0.0",
  "useNewtonsoft": "false",
  "sourceFolder": ""
}

Steps to reproduce

1. Create file device_registration_api.yaml containing the OpenAPI declaration
2. Create file openApiGeneratorConfig.json containing the generation details
3. Run openapi-generator-cli generate -i .\device_registration_api.yaml -g aspnetcore -c .\openApiGeneratorConfig.json -o .\out
4. Open file out/DeviceRegistrationApi/Controllers/APIApi.cs, which contains the line using DeviceRegistrationApi.Models;, however namespace Models does not exist and thus building the application will fail.

Related issues/PRs

No related issues found

Suggest a fix

As no models are specified in the OpenAPI file, no models are generated and thus no Models namespace exists, which is correct. So the controllers should not have a namespace to Models, however the generator still adds a reference, which is wrong. I assume, controller generation does not check if there were models generated.

Reproduce the issue with device_registration_api.yaml and openApiGeneratorConfig.json using the listed aspnetcore generation command. Inspect out/DeviceRegistrationApi/Controllers/APIApi.cs and verify the generated project when no models exist. Done means the controller does not reference the nonexistent DeviceRegistrationApi.Models namespace and the output builds successfully.