Enforce Empty List, Set, Map on Table Rows in

[clun]

The intrinsic "ambiguity" down at the Cassandra level, paired with the Data API omitting nulls, made it possible for clients to decide how to resolve this ambiguity, and we thought it more convenient to reconstruct these types as empty lists/sets/maps (which does not contradict the nulls from DB, yet is more consistent with the column type)

• Given a row return from the DB,``
• If the return value is NULL
• but the type describe in the schema told it is a list, set or map
• populate the attribute with an empty list

[clun]

Test implementations

public void should_findOne_with_null_collections() {
        String tableName = "table_null_collections";
        getDatabase().dropTable(tableName, IF_EXISTS);

        // Create table with UUID pk, a scalar, and LIST / SET / MAP columns
        Table<Row> table = getDatabase().createTable(tableName, new TableDefinition()
                .addColumn("id", TableColumnTypes.UUID)
                .addColumnText("label")
                .addColumnList("tags", TableColumnTypes.TEXT)
                .addColumnSet("categories", TableColumnTypes.TEXT)
                .addColumnMap("properties", TableColumnTypes.TEXT, TableColumnTypes.INT)
                .partitionKey("id"), IF_NOT_EXISTS);

        // Insert a row with ONLY the pk and scalar — list, set, map are omitted (null in Cassandra)
        UUID rowId = UUID.randomUUID();
        table.insertOne(new Row()
                .addUUID("id", rowId)
                .addText("label", "row_with_nulls"));

        // --- findOne: null collection columns should come back as empty, not null ---
        Optional<Row> result = table.findOne(Filters.eq("id", rowId));
        assertThat(result).isPresent();
        Row row = result.get();
        assertThat(row.getText("label")).isEqualTo("row_with_nulls");

        // LIST column → empty list (not null)
        Object tags = row.getColumnMap().get("tags");
        assertThat(tags).isNotNull().isInstanceOf(List.class);
        assertThat((List<?>) tags).isEmpty();

        // SET column → empty set (not null)
        Object categories = row.getColumnMap().get("categories");
        assertThat(categories).isNotNull().isInstanceOf(Set.class);
        assertThat((Set<?>) categories).isEmpty();

        // MAP column → empty map (not null)
        Object properties = row.getColumnMap().get("properties");
        assertThat(properties).isNotNull().isInstanceOf(Map.class);
        assertThat((Map<?, ?>) properties).isEmpty();

        log.info("findOne: null LIST/SET/MAP returned as empty collections");

        // --- findPage (via find cursor): same behavior ---
        List<Row> rows = table.find(Filters.eq("id", rowId)).toList();
        assertThat(rows).hasSize(1);
        Row pageRow = rows.get(0);
        assertThat(pageRow.getColumnMap().get("tags")).isNotNull().isInstanceOf(List.class);
        assertThat((List<?>) pageRow.getColumnMap().get("tags")).isEmpty();
        assertThat(pageRow.getColumnMap().get("categories")).isNotNull().isInstanceOf(Set.class);
        assertThat((Set<?>) pageRow.getColumnMap().get("categories")).isEmpty();
        assertThat(pageRow.getColumnMap().get("properties")).isNotNull().isInstanceOf(Map.class);
        assertThat((Map<?, ?>) pageRow.getColumnMap().get("properties")).isEmpty();

        log.info("find (cursor): null LIST/SET/MAP returned as empty collections");

        // --- Row with actual values should still come back correctly ---
        UUID rowId2 = UUID.randomUUID();
        table.insertOne(new Row()
                .addUUID("id", rowId2)
                .addText("label", "row_with_values")
                .addList("tags", List.of("java", "sdk"))
                .addSet("categories", Set.of("open-source", "database"))
                .addMap("properties", Map.of("priority", 1, "version", 2)));

        Optional<Row> result2 = table.findOne(Filters.eq("id", rowId2));
        assertThat(result2).isPresent();
        Row row2 = result2.get();
        @SuppressWarnings("unchecked")
        List<String> tagValues = (List<String>) row2.getColumnMap().get("tags");
        assertThat(tagValues).containsExactlyInAnyOrder("java", "sdk");
        // API returns SET as JSON array (ArrayList); verify contents via new Set
        @SuppressWarnings("unchecked")
        List<String> categoryRaw = (List<String>) row2.getColumnMap().get("categories");
        assertThat(new HashSet<>(categoryRaw)).containsExactlyInAnyOrder("open-source", "database");
        @SuppressWarnings("unchecked")
        Map<String, Integer> propValues = (Map<String, Integer>) row2.getColumnMap().get("properties");
        assertThat(propValues).containsEntry("priority", 1).containsEntry("version", 2);

        log.info("findOne: non-null LIST/SET/MAP returned with correct values");

        // Cleanup
        getDatabase().dropTable(tableName, IF_EXISTS);
    }