docs: def values():
      """Get the full current set of B3 values.
      :return: A dict containing the keys "X-B3-TraceId", "X-B3-ParentSpanId", "X-B3-SpanId", "X-B3-Sampled" and
      "X-B3-Flags" for the current span or subspan. NB some of the values are likely be None, but
      all keys will be present.
      """
      result = {}
      try:
          # Check if there's a sub-span in progress, otherwise use the main span:
          span = g.get("subspan") if "subspan" in g else g
          for header in b3_headers:
              result[header] = span.get(header)
      except RuntimeError:
          # We're probably working outside the Application Context at this point, likely on startup:
          # https://stackoverflow.com/questions/31444036/runtimeerror-working-outside-of-application-context
          # We return a dict of empty values so the expected keys are present.
          for header in b3_headers:
              result[header] = None
  
      return result