ng-swagger-gen not working with custom templates

[ABogd]

Command:
npx ng-swagger-gen -i some-api-1.0.0.yaml -o apis/some-api -c my-ng-swagger-gen-config.json
Content of my-ng-swagger-gen-config.json:

{
  "templates": "apis/src/templates"
}

apis/src/templates contains a file configuration.mustache, which is a copy of https://github.com/cyclosproject/ng-swagger-gen/blob/master/templates/configuration.mustache
Result of running the command:
Error: TypeError: Invalid template! Template should be a "string" but "undefined" was given as the first argument for mustache#render(template, view, partials)

The corresponding configuration works without any problem for ng-openapi-gen.