message: Remove invalid exception in linear operator
diff: @@ -478,7 +478,6 @@ class LinearOperator(object):
  cond,
  self._max_condition_number_to_be_non_singular(),
  message="Singular matrix up to precision epsilon.")
  - raise NotImplementedError("assert_non_singular is not implemented.")
  def _max_condition_number_to_be_non_singular(self):
  """Return the maximum condition number that we consider nonsingular."""
  