code: def _get_trusted_comma(self, trusted, value):
          
          if not (trusted and value):
              return
          values = [x.strip() for x in value.split(",")]
          if len(values) >= trusted:
              return values[-trusted]
docs: Get the real value from a comma-separated header based on the
          configured number of trusted proxies.
  
          :param trusted: Number of values to trust in the header.
          :param value: Header value to parse.
          :return: The real value, or ``None`` if there are fewer values
              than the number of trusted proxies.
  
          .. versionadded:: 0.15