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