presto-main/src/main/java/io/prestosql/metadata/QualifiedTablePrefix.java/QualifiedTablePrefix/asSchemaTablePrefix
class QualifiedTablePrefix:    public SchemaTablePrefix asSchemaTablePrefix()
    {
        if (!schemaName.isPresent()) {
            return new SchemaTablePrefix();
        }
        else if (!tableName.isPresent()) {
            return new SchemaTablePrefix(schemaName.get());
        }
        else {
            return new SchemaTablePrefix(schemaName.get(), tableName.get());
        }
    }