public Item withMap(String attrName, Map<String, ?> val) {
        checkInvalidAttribute(attrName, val);
        attributes.put(attrName, valueConformer.transform(val));
        return this;
    }
Sets the value of the specified attribute in the current item to the
given value.
aws-java-sdk-dynamodb/src/main/java/com/amazonaws/services/dynamodbv2/document/Item.java