Plugins/docker empty build_args in jsonnet

I’m trying out the jsonnet feature by converting an existing yaml and so far so good, however I have an issue – I’m reusing some function in a monorepo and I have this:

local DockerRepoSettings(name, dockerfile, context=null, build_args=[]) = {
  repo: 'xxx/' + name,
  registry: 'xxxx',
  username: 'xxx',
  password: 'xxxxx,
  context: if context != null then context else name,
  dockerfile: dockerfile,
  build_args: build_args,

and in step:

        name: 'build-and-push',
        image: 'plugins/docker',
        settings: DockerRepoSettings(name='xxx', dockerfile='xxx/Dockerfile'),

so when build_args is not specified I expect it to be an empty array and get ignored by plugins/docker, however:

usr/local/bin/docker build --rm=true -f xxx/Dockerfile -t 118f8043074a8d82c2cb2dcd6044009b5149e1e1 xxx --pull=true --build-arg --label org.opencontainers.image.created=2022-04-30T00:01:21Z ...

resulting in:

invalid argument "" for "--build-arg" flag: invalid environment variable: 
See 'docker build --help'.
exit status 125

I tried some other syntax but it seems I cannot skip the --build-arg docker argument if array is empty.

any tips?

switched to kaniko and it seems to work fine, weird, the args logic seems pretty much the same