@Override
    public Object unmarshall(AttributeValue value) {
        Set<BigInteger> result = new HashSet<BigInteger>();
        for (String s : value.getNS()) {
            result.add(new BigInteger(s));
        }
        return result;
    }
An unmarshaller that unmarshals DynamoDB NumberSets into sets of Java
{@code BigInteger}s.
aws-java-sdk-dynamodb/src/main/java/com/amazonaws/services/dynamodbv2/datamodeling/unmarshallers/BigIntegerSetUnmarshaller.java