public AddAction append(Number... values) {
        return append(new LinkedHashSet<Number>(Arrays.asList(values)));
    }
Returns an <code>AddAction</code> for building expression that would
append the specified values to this number set; or if the attribute does
not already exist, adding the new attribute and the value(s) to the item.
<p>
In general, DynamoDB recommends using SET rather than ADD.
aws-java-sdk-dynamodb/src/main/java/com/amazonaws/services/dynamodbv2/xspec/NS.java