message: If FTT not given, use 1/3 of validators' weights.
diff: @@ -598,7 +598,6 @@ impl<C: Context<ValidatorId = ValidatorId>, DS: Strategy<DeliverySchedule>>
  self.faulty_num
  };
  - let ftt = self.ftt.ok_or_else(|| BuilderError::EmptyFtt)?;
  let instance_id = self.instance_id.clone();
  let seed = self.seed;
  let round_exp = self.round_exp;
  @@ -614,6 +613,14 @@ impl<C: Context<ValidatorId = ValidatorId>, DS: Strategy<DeliverySchedule>>
  Distribution::Poisson(_) => unimplemented!("Poisson distribution of weights"),
  };
  + let ftt = match self.ftt {
  + None => {
  + let weights_sum = weights.iter().fold(0u64, |acc, el| acc + el.0);
  + weights_sum / 3
  + }
  + Some(ftt) => ftt,
  + };
  +
  let validator_ids = (0..validators_num)
  .map(|i| ValidatorId(i as u64))
  .collect::<Vec<_>>();
  