presto-client/src/main/java/io/prestosql/client/NamedClientTypeSignature.java/NamedClientTypeSignature/toString
class NamedClientTypeSignature:    @Override
    public String toString()
    {
        if (fieldName.isPresent()) {
            return format("%s %s", fieldName.get(), typeSignature);
        }
        return typeSignature.toString();
    }