code: def _push_image(
      self,
      tag: str,
      registry_url: Optional[str] = None,
      username: Optional[str] = None,
      password: Optional[str] = None,
  ) -> str:
      with contextlib.closing(docker.from_env()) as client:
          if registry_url and username and password:
              client.login(
                  username=username,
                  password=password,
                  registry=registry_url,
              )
  
          result = client.images.push(repository=tag)
          return result
  
imports: import contextlib
  import io
  import os.path
  from pathlib import Path
  from typing import Any
  from typing import Iterable
  from typing import Optional
  from typing import Tuple
  import docker
  from docker.models.images import Image
  from .config import CustomWorkerConfig
  from .config import DockerWorkerConfig
  from .config import WorkerConfig
label_desc: Use image node_id 6 for calling the CustomWorkerBuilder obj's underlying member method code with example usage: obj._push_image(tag, registry_url, username, password) and returns: result