public Item withList(String attrName, Object ... vals) {
        checkInvalidAttribute(attrName, vals);
        List<Object> list_in = Arrays.asList(vals);
        attributes.put(attrName, valueConformer.transform(list_in));
        return this;
    }
Sets the value of the specified attribute in the current item to the
given values as a list.
aws-java-sdk-dynamodb/src/main/java/com/amazonaws/services/dynamodbv2/document/Item.java