Metadata request behaviour change after upgrading from 11.4.7 to 11.4.8

@Test

public void testDefault() throws SQLException {

    var dataSource = DATA_SOURCE;

    var connection = dataSource.getConnection();

    var metadata = connection.getMetaData();

    var catalog = connection.getCatalog();

    var schema = connection.getSchema();

    try (var resultSet = metadata.getColumns(catalog, schema, TABLE, COLUMN)) {

        resultSet.next();

        var defaultValue = resultSet.getString("COLUMN_DEF");

        assertNull(defaultValue);

        // Passed on 11.4.7

        //

        // FAILED on 11.4.8 because instead of null it returns 'NULL' (string):

        // org.opentest4j.AssertionFailedError:

        // Expected :null

        // Actual   :NULL

    } finally {

        close(connection, dataSource);

    }

}