code: def pre_dissect(self, s):
          
          length = len(s)
          if length < _BGP_CAPABILITY_MIN_SIZE:
              err = " ({}".format(length) + " is < _BGP_CAPABILITY_MIN_SIZE "
              err += "({})).".format(_BGP_CAPABILITY_MIN_SIZE)
              raise _BGPInvalidDataException(err)
          return s
docs: Check that the payload is long enough (at least 2 bytes).