DynamoDB enhanced client: TableSchema<T>.attributeValue method throws NullPointerException when retrieving value of an attribute of a flattened model  #4218

@DynamoDbBean
public class FlattenedModel {
    private String attribute;

    public FlattenedModel() {
    }

    public FlattenedModel(String attribute) {
        this.attribute = attribute;
    }

    public String getAttribute() {
        return attribute;
    }

    public void setAttribute(String attribute) {
        this.attribute = attribute;
    }
}

@DynamoDbBean
public class Model {
    private FlattenedModel flattenedModel;

    public Model() {
    }

    public Model(FlattenedModel flattenedModel) {
        this.flattenedModel = flattenedModel;
    }

    @DynamoDbFlatten
    public FlattenedModel getFlattenedModel() {
        return flattenedModel;
    }

    public void setFlattenedModel(FlattenedModel flattenedModel) {
        this.flattenedModel = flattenedModel;
    }
}

public class Main {
    public static void main(String[] args)  {
        TableSchema<Model> schema = TableSchema.fromClass(Model.class);
        var model = new Model();
        model.setFlattenedModel(new FlattenedModel(null));
        var value = schema.attributeValue(model, "attribute");
    }
}