private static List<ValueConstraint[]> antecedentsReturning(List<PreContract> values, ContractReturnValue result) {
    return ContainerUtil.mapNotNull(knownContracts(values),
                                    contract -> contract.getReturnValue().equals(result) ?
                                                contract.getConstraints().toArray(new ValueConstraint[0]) : null);
  }
private static List<ValueConstraint[]> antecedentsReturning(List<PreContract> values, ContractReturnValue result)