presto-blackhole/src/main/java/io/prestosql/plugin/blackhole/BlackHoleMetadata.java/BlackHoleMetadata/createSchema
class BlackHoleMetadata:    @Override
    public synchronized void createSchema(ConnectorSession session, String schemaName, Map<String, Object> properties)
    {
        if (schemas.contains(schemaName)) {
            throw new PrestoException(ALREADY_EXISTS, format("Schema [%s] already exists", schemaName));
        }
        schemas.add(schemaName);
    }