docstr: Adds extra_env to env.
  
  :param env: dict representing environment variables
  :param extra_env: additional variables to be added to env
docstr_tok: ["Adds","extra_env","to","env",".",":","param","env",":","dict","representing","environment","variables",":","param","extra_env",":","additional","variables","to","be","added","to","env"]
code: def _add_envs(self, env, extra_env):
      """
      Adds extra_env to env.
  
      :param env: dict representing environment variables
      :param extra_env: additional variables to be added to env
      """
      for key, value in extra_env.items():
          if value is None:
              if key in env:
                  del env[key]
          else:
              env[key] = value
  
imports: import abc
  import threading
  from horovod.runner.common import util
  from horovod.runner.common.util import network, safe_shell_exec, timeout
  from horovod.runner.util.streams import Pipe
  from horovod.runner.util.threads import in_thread
label_desc: Use image node_id 3 for calling the BasicTaskService obj's underlying member method code with example usage: obj._add_envs(env, extra_env) without return types