@NotNull
  public static MethodContract singleConditionContract(ContractValue left,
                                                       RelationType relationType,
                                                       ContractValue right,
                                                       ContractReturnValue returnValue) {
    return singleConditionContract(ContractValue.condition(left, relationType, right), returnValue);
  }
@NotNull
  public static MethodContract singleConditionContract(ContractValue left,
                                                       RelationType relationType,
                                                       ContractValue right,
                                                       ContractReturnValue returnValue)