public BigInteger getBigInteger(String attrName) {
        BigDecimal bd = getNumber(attrName);
        return bd == null ? null : bd.toBigInteger();
    }
Returns the value of the specified attribute in the current item as an
<code>BigInteger</code>; or null if the attribute doesn't exist.

@see #isNull(String) #isNull(String) to check if the attribute value is
     null.
@see #isPresent(String) #isPresent(String) to check if the attribute
     value is present.

@throws NumberFormatException
            if the attribute value is null or not a valid representation
            of a {@code BigDecimal}.
aws-java-sdk-dynamodb/src/main/java/com/amazonaws/services/dynamodbv2/document/Item.java