presto-kafka/src/main/java/io/prestosql/plugin/kafka/KafkaMetadata.java/KafkaMetadata/listSchemaNames
class KafkaMetadata:    @Override
    public List<String> listSchemaNames(ConnectorSession session)
    {
        ImmutableSet.Builder<String> builder = ImmutableSet.builder();
        for (SchemaTableName tableName : tableDescriptions.keySet()) {
            builder.add(tableName.getSchemaName());
        }
        return ImmutableList.copyOf(builder.build());
    }