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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _POUpdateBuilderWrapper(env, target=None, source=_null, **kw):
 """ Wrapper for `POUpdate` builder - make user's life easier """

  if source is _null:
    if 'POTDOMAIN' in kw:
      domain = kw['POTDOMAIN']
    elif 'POTDOMAIN' in env and env['POTDOMAIN']:
      domain = env['POTDOMAIN']
    else:
      domain = 'messages'
    source = [ domain ] # NOTE: Suffix shall be appended automatically
  return env._POUpdateBuilder(target, source, **kw)