code: public TransactionWriteRequest addConditionCheck(Object key,
                                                       DynamoDBTransactionWriteExpression transactionWriteExpression,
                                                       ReturnValuesOnConditionCheckFailure returnValuesOnConditionCheckFailure) {
          transactionWriteOperations.add(new TransactionWriteOperation(key, TransactionWriteOperationType.ConditionCheck, transactionWriteExpression, returnValuesOnConditionCheckFailure));
          return this;
      }
docs: Adds conditionCheck operation (to be executed on the object represented by key) to the list of transaction write operations.
  transactionWriteExpression is used to condition check on the object represented by key.
  returnValuesOnConditionCheckFailure specifies which attributes values (of existing item) should be returned if condition check fails.