DynamodbAttributeValueTransformer causing break in functionality for empty list when transforming (v2)

[8aemi]

I'm using DynamoDb Enhanced library version 2.15.82. Recently, aws-lambda-java-events-sdk-transformer version 3.0.2 causes a break in the functionality when trying to transform empty list. Empty list is transformed to null which for DynamoDb Enhanced library expects an empty list, and causes DynamoDB Enhanced library to throw the below stack trace.

java.lang.IllegalStateException: Unable to convert attribute value: AttributeValue()
software.amazon.awssdk.enhanced.dynamodb.internal.converter.attribute.EnhancedAttributeValue.fromAttributeValue(EnhancedAttributeValue.java:352) ~[dynamodb-enhanced-2.15.82.jar:na]
software.amazon.awssdk.enhanced.dynamodb.internal.converter.attribute.ListAttributeConverter$Delegate.transformTo(ListAttributeConverter.java:154) ~[dynamodb-enhanced-2.15.82.jar:na]
software.amazon.awssdk.enhanced.dynamodb.internal.converter.attribute.ListAttributeConverter.transformTo(ListAttributeConverter.java:120) ~[dynamodb-enhanced-2.15.82.jar:na]
software.amazon.awssdk.enhanced.dynamodb.internal.converter.attribute.ListAttributeConverter.transformTo(ListAttributeConverter.java:82) ~[dynamodb-enhanced-2.15.82.jar:na]
software.amazon.awssdk.enhanced.dynamodb.internal.mapper.StaticAttributeType.attributeValueToObject(StaticAttributeType.java:44) ~[dynamodb-enhanced-2.15.82.jar:na]
software.amazon.awssdk.enhanced.dynamodb.internal.mapper.ResolvedImmutableAttribute.lambda$create$1(ResolvedImmutableAttribute.java:61) ~[dynamodb-enhanced-2.15.82.jar:na]
software.amazon.awssdk.enhanced.dynamodb.mapper.StaticImmutableTableSchema.mapToItem(StaticImmutableTableSchema.java:458) ~[dynamodb-enhanced-2.15.82.jar:na]
software.amazon.awssdk.enhanced.dynamodb.mapper.WrappedTableSchema.mapToItem(WrappedTableSchema.java:54) ~[dynamodb-enhanced-2.15.82.jar:na]

Further investigation points to the below code in DynamodbAttributeValueTransformer that's causing the issue

else if (Objects.nonNull(value.getL())) {
            return AttributeValue.builder()
                    .l(value.getL().isEmpty()
                            ? null
                            : value.getL().stream()
                                .map(DynamodbAttributeValueTransformer::toAttributeValueV2)
                                .collect(Collectors.toList()))
                    .build();

        }

I noticed this change happens from aws-lambda-java-events-sdk-transformer version 2.0.8 to 3.0.0 on commit 3e71a17c57ba6c99734c4633a4f412fd2d5b6b42

Any advice on this? Is there a reason for this code change that causes a break in functionality?

[acmcelwee]

I just came here to open an issue on the v1 transformer for this same behavior. In our case, the AWS-owned ItemUtils::toSimpleValue is where it's blowing up for us. By coercing an empty list to a null value, the AttributeValue data type is no longer discernible.

[productivityindustries]

Same issue here. The conversion produces item maps which are not deserializable to Java objects. This is quite a blocker for me, I wonder why no one is still looking at the issue.