presto-main/src/main/java/io/prestosql/connector/system/DelegatingSystemTablesProvider.java/DelegatingSystemTablesProvider/getSystemTable
class DelegatingSystemTablesProvider:    @Override
    public Optional<SystemTable> getSystemTable(ConnectorSession session, SchemaTableName tableName)
    {
        return delegates.stream()
                .map(delegate -> delegate.getSystemTable(session, tableName))
                .filter(Optional::isPresent)
                // this ensures there is 0 or 1 element in stream
                .map(Optional::get)
                .collect(toOptional());
    }